Contents
Fully compliant

EN ISO 19403-3 paints and varnishes, wettability part 3: determination of the surface tension of liquids using the pendant drop method

Measure the surface tension of a paint, varnish or other liquid coating from the shape of a hanging drop, the method EN ISO 19403-3 describes. Lower values usually mean the liquid wets a substrate more easily. The Dropometer runs this measurement up to 75 mN/m with ±0.03 mN/m accuracy (Dropometer datasheet).

What brings you here?

Who this is for
Paint and coating formulators, raw material suppliers and QC labs who check the surface tension of liquid coatings.
Compliance tier
Fully compliant: the Dropometer measures pendant drop surface tension with a Young-Laplace fit, as this method describes.
Measurement
Pendant drop surface tension up to 75 mN/m, ±0.03 mN/m accuracy, 0.01 mN/m resolution (Dropometer datasheet).
Setup
About 2 minutes. Battery powered, 1 kg. No temperature control, so test in a conditioned room.
Last updated
October 20, 2026
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Free one page checklist for EN ISO 19403-3: what to prepare, the settings to lock, how many drops to measure and what to record. Made for paint and coatings QC benches.

Talk to an expert

Book a 15 minute demo on your coating liquid

Tell us your coating, its solvent and your current surface tension check. We will measure a pendant drop live and tell you plainly where the Dropometer fits your QC plan and where it does not.

Book a 15 minute demo
View the official standard
Gurdeep-Saini-Photo
Written by
Gurdeep Singh Saini
Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.
COO at Droplet Lab
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Droplet-Lab logo
Technical Review by
Droplet Lab Team
Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.
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Verified against EN ISO 19403-3
Gurdeep-Saini-Photo
Written By

Gurdeep Singh Saini

COO at Droplet Lab

Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.

Droplet-Lab logo
Reviewed By

Droplet Lab Team

Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.

Featured Studies & Publications

Research Paper Contact angle measurement with a smartphone
Research Paper Surface tension measurement with a smartphone using a pendant drop

Evidence box: EN ISO 19403-3 part 3 and the Dropometer

Standard

ISO 19403-3:2024, Paints and varnishes: Wettability: Part 3: Determination of the surface tension of liquids using the pendant drop method, from ISO/TC 35/SC 9. It replaces the 2017 edition and is adopted in Europe as EN ISO 19403-3:2024. See the ISO listing.

Compliance tier

Fully compliant. The Dropometer forms a pendant drop, fits the Young-Laplace equation to its outline and reports surface tension, which is what this method reads. The method sets laboratory test conditions rather than a heated or cooled cell, so the Dropometer runs it in a conditioned room.

Instrument performance

Surface tension up to 75 mN/m, accuracy ±0.03 mN/m, resolution 0.01 mN/m, static and dynamic, from the Dropometer product specification.

Peer reviewed method

The drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers, one of them on pendant drop surface tension. See our validation publications.

Customer evidence

We have no published client work on paint or coating liquids yet. Bring your own samples to a 15 minute demo and judge the readings yourself.

What it does not tell you

Liquid surface tension alone does not predict wetting. It must be compared with the surface free energy of the substrate, and it does not measure adhesion of the dried film.

Executive summary

What this standard measures, who uses it and how the Dropometer fits

EN ISO 19403-3 measures the surface tension of paints, varnishes and other liquid coating materials with the pendant drop method: a drop hangs from a needle and its shape gives the value. Coating formulators, raw material suppliers and paint QC labs use it to release batches and compare formulations. The Dropometer is fully compliant with this measurement and reads surface tension up to 75 mN/m with ±0.03 mN/m accuracy (Dropometer datasheet).

The method fits the Young-Laplace equation to the drop outline, using the density difference between the liquid and the air around it. You repeat the reading on several drops and report the mean with its spread. The current edition is ISO 19403-3:2024, adopted in Europe as EN ISO 19403-3:2024. Part 2 of the series covers the surface free energy of solids, and Part 4 the polar and dispersive fractions of a liquid. Our surface tension measurement guide explains the physics, and reproducible surface tension measurement covers the habits that keep results comparable between operators.

The Dropometer pendant drop tensiometer runs on battery and sets up in about 2 minutes, so it can sit in the QC lab or beside the mixing area. It has no temperature control, so you test in a conditioned room and record the temperature with every result. Our experiment on the surface tension of water and temperature shows why that record matters. If a print or coating line shows beading, see ink beading and viscosity troubleshooting.

Further reading: the paint guide, why contact angle matters for coatings and adhesives QC, the glossary entry on dynamic surface tension, our guide to the best tensiometer for dynamic surface tension and our open dataset of client collected wetting measurements.

How the Dropometer fits: using the pendant drop method step by step

The EN ISO 19403-3 measurement, step by step, in our own words

From coating sample to a recorded surface tension

These steps outline the procedure. They do not replace the standard. Buy the current edition and follow its needle, drop shape, density and test condition rules.

±0.03 mN/m

Surface tension accuracy

From the Dropometer product specification. Resolution is 0.01 mN/m.

Up to 75 mN/m

Measuring range

Covers solventborne and waterborne coatings, and pure water as a system check.

About 2 min

Setup

Base plate, phone holder, LED and syringe. No PC needed.

1

Prepare the liquid

Mix the sample as your SOP describes and let trapped air escape. Bring it to the test temperature in the conditioned room. Look up or measure its density at that temperature, as the standard specifies.

2

Set up the Dropometer

Place the base plate on a level bench away from draughts, vibration and strong light. Mount the phone and LED, fit a clean needle of the size the standard allows, and fill the syringe without bubbles.

3

Lock focus and scale

Focus on the needle tip and set the image scale. Do not change focus or zoom after that, or the scale no longer matches. Limit evaporation of volatile liquids as the standard describes.

4

Form the pendant drop

Dispense a large drop that still hangs steadily from the needle. It must be symmetrical about its vertical axis. The standard sets a drop shape criterion, so choose the needle and drop size to meet it.

5

Capture and fit

Enter the density difference and capture the drop. The software fits the Young-Laplace equation to the outline, and automatic edge detection gives the same reading from the same image. Reject drops that are not symmetrical or fit poorly.

6

Repeat and record

Measure fresh drops, at least as many as the standard specifies. Record the mean, spread, density and its source, temperature, humidity, needle and test date. For habits that keep results comparable, see reproducible surface tension measurement.

7

Watch the full measurement

This video shows a complete Dropometer pendant drop surface tension measurement, from setup to result. It covers the steps above in one run.

Dropometer pendant drop surface tension, start to finish.

Validated measurement approach

Independent benchmarking and publication-based validation references.

Peer reviewed method

The Dropometer drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers, one in Review of Scientific Instruments and one in Colloids and Surfaces A. Datasheet surface tension accuracy is ±0.03 mN/m.

Read the validation papers

Customer evidence

We have no published client work on paint or coating liquids yet. The fairest test is your own sample: bring a retained reference and a problem batch to a demo.

Book a 15 minute demo

Set limits for paints and varnishes from your own liquids

EN ISO 19403-3 · batch release · coatings QC

EN ISO 19403-3 tells you how to measure surface tension. It does not tell you what value a good batch should have. The standard includes precision data from an interlaboratory study, which helps you judge how much difference between two results is real. Use the figures in the current edition.

Set your accept band from your own correlation study. Keep a retained reference batch, measure batches that levelled and wetted well and batches that cratered or crawled, then place your limits between them. Many labs express the band as a difference from the retained reference rather than a fixed value.

Check the setup with pure water before a study and compare the result with a published value at your test temperature. Our water and temperature experiment shows how much the value moves with temperature. Repeat the study when you change resin, surfactant, solvent blend or supplier.

Example output

Example data for illustration only. These are not measured results. Your own coating, test temperature and limits decide the numbers.

Example: waterborne clearcoat batches against a retained reference

Sample Drops (n) Mean surface tension (mN/m) Std dev (mN/m) Difference from reference (mN/m) Decision
Retained reference532.40.20.0Reference
Batch 2417532.70.3+0.3Accept
Batch 2418533.60.4+1.2Review, measure again
Batch 2419536.10.3+3.7Hold, check surfactant dosing

How to read this table

Each row is the mean of five pendant drops of one batch, measured in the same conditioned room at the same recorded temperature. The decision column uses an example accept band of ±1.0 mN/m around the retained reference and an example hold limit of 2.0 mN/m, both set from a correlation study.

Example output chart

The same example data as the table, plotted against the retained reference and the example accept band and hold limit.

Bar chart of example pendant drop surface tension for a retained reference and three clearcoat batches, with an example accept band of 31.4 to 33.4 mN/m and a hold limit at 34.4 mN/m

Example data, not measured results.

Business impact

What changes when the check is a pendant drop reading

Metric Before Dropometer With Dropometer Results
How the check is made Ring or plate tensiometer in a shared lab Pendant drop read from the drop image No published benchmark
Sample needed A filled vessel of liquid One drop at a time from the syringe No published benchmark
Result format A value read off the instrument Surface tension per drop, 0.01 mN/m resolution, ±0.03 mN/m accuracy Dropometer product specification
Where it runs Central lab only QC bench or beside the mixing area, on battery for up to 8 h Dropometer product specification

See the measurement on your own coating

Bring a retained reference and a batch that caused trouble. We will measure both live.

Book a 15 minute demo Request a quote
ROI estimate

Estimate the cost of the coating defects this test can catch

Enter your own numbers. The defaults are examples, not Droplet Lab results.

Quality cost snapshot

Estimate what wetting related failures cost you.

Example only. Use what you see in a trial on your own samples.
Your own figure.
Your own estimate.

Result

~0
Estimated annual cost today
~0
Estimated annual cost avoided
~0
Payback period

Annual exposure combines audit/CAPA cost, customer rejections, and recall probability; avoided exposure applies the risk reduction percentage.

Method settings for surface tension of liquids using the pendant drop

Lock these before you compare results between shifts or sites

Parameter Recommended Setting Technical Rationale
Measurement Pendant drop, static reading The method reads a drop hanging steadily from a needle.
Fit model Young-Laplace The method evaluates the drop outline with the Young-Laplace equation. Use the same model for every run.
Needle Size the standard allows, diameter known Liquids with high surface tension or low density need a larger needle to give a usable drop shape.
Drop size and shape Large, steady, symmetrical, within the standard's shape criterion A drop that is too round or too small carries little shape information and fits poorly.
Density Liquid and air density at the test temperature, source recorded The result scales with the density difference, so a wrong density gives a wrong value.
Replicates At least the number of drops the standard specifies One drop does not show contamination or drift. Report the mean and the spread.
Test conditions Conditioned room as the standard specifies; record temperature and humidity The Dropometer runs at 10 to 45 °C and has no temperature control, so the room sets the temperature.
Image scale Set after final focus and zoom, then left alone Changing focus or zoom after scaling shifts every result.

Is ISO 19403-3 the right test?

Pick the method by the question you need answered

Start: What do you need to know about your coating?

Surface tension of the liquid coating

Signals:

You want a number per batch for release, supplier checks or formulation work.

Rule-out:

Use EN ISO 19403-3, this page. The Dropometer is fully compliant.

How surfactants act over time

Signals:

Fast processes such as spraying or printing depend on how quickly the surface tension falls after a new surface forms.

Rule-out:

Measure dynamic surface tension with a time resolved pendant drop. The Dropometer reads from about 0.1 s, not the millisecond range.

Surface free energy of the substrate or dried film

Signals:

You need to know whether the substrate can be wetted by your coating at all.

Rule-out:

Use contact angles with several test liquids, as in ISO 19403-2.

Polar and dispersive parts of the liquid

Signals:

You need to split the liquid's surface tension into its polar and dispersive parts.

Rule-out:

The polar and dispersive fractions of the surface tension are covered by Part 4 of the ISO 19403 series, which uses a two liquid method the Dropometer does not run.

Decision tree at a glance

Start from the question you need answered. Blue boxes are measurements the Dropometer runs.

Decision tree for choosing between EN ISO 19403-3 pendant drop surface tension, dynamic pendant drop, ISO 19403-2 contact angles and the ISO 19403-4 two liquid method

Is ISO 19403-3 the right test?

Interpreting surface tension and wettability

What the surface tension tells you, and what it does not

Lower than the substrate, better wetting: A coating wets well when its surface tension sits below the surface free energy of the substrate.
Drift from the reference points to the recipe: A batch reading higher than the retained reference often means less surfactant or a different solvent balance.
Spread between drops is a signal: High scatter points to contamination, evaporation, a drop that has not settled or a liquid with a yield point.
Surface tension is not adhesion: A good value shows the liquid can wet. It does not prove the dried film will bond or level.
Expert perspective

Why surface tension decides how a coating wets

Plot surface tension against surfactant concentration and the interface tells you when it is saturated: the curve bends at the point where the surface can hold no more.

Dr. Alidad Amirfazli

Department of Mechanical Engineering, York University, Co-founder and Scientific Advisor, Droplet Lab

Common pitfalls and limits

Honest limits of the method and of the Dropometer

The standard notes that applicability can be restricted for liquids with non Newtonian flow behaviour. Thixotropic paints or liquids with a yield point may not reach a true drop shape.
Solvents evaporate from the drop surface and change the reading. Work quickly and limit evaporation as the standard describes.
The Dropometer has no temperature control. Test in a conditioned room, let samples reach room temperature and record it.
The Dropometer reads surface tension up to 75 mN/m. Liquids above that are outside its range.
The camera runs at 10 frames per second. That suits static readings and dynamic readings from about 0.1 s, not millisecond surfactant studies.
FAQ

Frequently asked questions

What does EN ISO 19403-3 measure?

It measures the surface tension of a liquid, such as a paint, varnish or other liquid coating, from the shape of a pendant drop. The drop outline is fitted with the Young-Laplace equation using the density difference between the liquid and air. The result is in mN/m.

Is EN ISO 19403-3 the same as ISO 19403-3?

Yes. EN ISO 19403-3:2024 adopts ISO 19403-3:2024 without technical change, and national versions such as DIN EN ISO 19403-3 follow it. The 2024 edition replaces the 2017 edition. Quote the designation and year your customer names in the specification.

Does ISO 19403-3 need a heated or cooled test cell?

From our reading, no. The method sets laboratory test conditions and asks that the liquids reach the test temperature, rather than calling for a heated or cooled cell. The Dropometer has no temperature control, so test in a conditioned room and record the temperature. Check the current edition for the exact conditions.

Can the Dropometer run ISO 19403-3?

Yes. The Dropometer measures pendant drop surface tension with a Young-Laplace fit, up to 75 mN/m with ±0.03 mN/m accuracy (Dropometer datasheet). Buy the current edition, follow its needle, drop shape and density rules, and validate the method in your own lab.

Can I measure a thick or thixotropic paint?

With care. The standard notes restrictions for liquids that are not Newtonian. A paint with a yield point may hold a shape that is not set by surface tension alone, which shows up as scatter between drops. Compare such results only with the same paint measured the same way.

Is this static or dynamic surface tension?

EN ISO 19403-3 reads a drop hanging steadily, which is a static value. If spraying or printing depends on how fast surfactants act, also measure dynamic surface tension. The Dropometer reads both, with dynamic readings from about 0.1 s.

Legal note

This page summarises EN ISO 19403-3 in our own words and does not reproduce the standard. Buy the current edition from ISO or your national standards body before you write a procedure. Droplet Lab does not certify compliance. Your own method validation does.

View the official standard Book a 15 minute demo

How this page was created

Sources, review and tools

Transparency 4 checklist items
01

Sources

ISO 19403-3:2024 listing; DIN EN ISO 19403-3:2024-11 listing (DIN Media); SS-EN ISO 19403-3:2024 listing (SIS); EVS-EN ISO 19403-3:2024 listing, the Dropometer product specification and Droplet Lab validation papers.

02

Drafting assistance

Drafted with Claude (Anthropic) from the sources listed, then reviewed by Droplet Lab.

03

What we did not do

We did not copy text from the standard. Buy the current edition for the full procedure.

04

Last checked

October 2026

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References

1. EN ISO 19403-3:2024 / ISO 19403-3:2024. iso.org/standard/87263.html
2. DIN EN ISO 19403-3:2024-11 listing (DIN Media). dinmedia.de/en/standard/din-en-iso-19403-3/384404119
3. SS-EN ISO 19403-3:2024 listing (SIS). sis.se/en/produkter/paint-and-colour-industries/paints-and-varnishes/s
4. EVS-EN ISO 19403-3:2024 listing. evs.ee/en/evs-en-iso-19403-3-2024
5. Droplet Lab. Peer reviewed validation papers in Review of Scientific Instruments and Colloids and Surfaces A. dropletlab.com/validation/publications/
6. Droplet Lab. Dropometer product specification, 2026. dropletlab.com/products/dropometer/