# ISO 19840

Source: https://coatmentor.com/standards/iso-19840/ · Updated 2026-10-04

Measuring and accepting dry film thickness on rough (blast-cleaned) surfaces.

**Publisher**: ISO

**Area**: Application and film thickness

*Figure: ISO 19840: mean ≥ nominal, every reading ≥ 80 %, fewer than 20 % of readings between 80 % and 100 %.*

ISO 19840 says how to measure dry film thickness (DFT) on blast-cleaned steel and when a coat passes. It applies to nominal DFTs of 40 µm and above.

## Gauge set-up and the profile correction

The gauge is verified at zero and with foils on smooth steel. A correction value for the profile is then subtracted from each reading: 10 µm for a fine, 25 µm for a medium and 40 µm for a coarse ISO 8503-1 profile, and 25 µm when the profile is unknown and no uncoated sample is available.

## Sampling

The number of readings depends on the inspection area: 5 up to 1 m², 10 up to 3 m², 15 up to 10 m², 20 up to 30 m², 30 up to 100 m², then 10 more for each extra 100 m² or part of it. Areas above 1,000 m² are split.

## Acceptance

- The mean of the readings is at least the nominal DFT.
- Every reading is at least 80 % of the nominal DFT.
- Fewer than 20 % of the readings are between 80 % and 100 % of nominal.
- No reading is above the specified maximum.

Note: ISO 19840 is outside the CIP 1 syllabus.

**Use it:** [DFT acceptance calculator](https://coatmentor.com/calculators/dft-acceptance/)

**14** practice items in the members area mention ISO 19840 (CIP 2: 6 · FROSIO written: 8).

## Related

- **Concepts:** [Dry film thickness measurement](https://coatmentor.com/learn/dft-measurement/)
- **Standards:** [SSPC-PA 2](https://coatmentor.com/standards/sspc-pa-2/) · [ASTM D7091](https://coatmentor.com/standards/astm-d7091/) · [ISO 2808](https://coatmentor.com/standards/iso-2808/) · [ISO 8503](https://coatmentor.com/standards/iso-8503/)
- **Defects:** [Solvent entrapment and popping](https://coatmentor.com/defects/solvent-entrapment/)

## About this page

**Also published openly:** [DeFelsko: ISO 19840 sampling plan and acceptance](https://www.defelsko.com/coating-thickness/positector-6000-iso-19840).

This page describes the subject of ISO 19840 in our own words; it does not reproduce the standard. For the full text, buy the current edition from ISO. Checked on 2026-10-04; errors go in the [corrections log](https://coatmentor.com/method/). CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.