Converting NCS to RAL (and back)
An NCS code and a RAL code describe colour in different ways. You can calculate from one to the other, but the result is an approximation — never an equivalence. This page sets out how that calculation works, where it stops being reliable, and how to check the outcome before you put it in a specification.
The short answer
There is no official conversion table between NCS and RAL, and there cannot be one: they are two independently defined collections. What you can do is express both colours in measured values (CIELab) and find the closest match. How close that is comes down to a single number: ΔE. Below ΔE 1 almost nobody sees a difference; above ΔE 3 most people do.
How an NCS code is built up
NCS describes colour the way a person perceives it. In S 1030-B, 10 is the blackness, 30 the chromaticness and B the hue. Every code is a position in a system, so colours that sit next to each other in the system also look alike.
That makes NCS well suited to discussing and choosing colour: you can reason about what happens if you raise the blackness or shift the hue.
How a RAL code is built up
With RAL it depends on the collection. RAL Classic — the familiar four-digit codes such as 9010 and 7016 — is a numbered collection that has grown since 1927. The first digit says something about the colour group, but beyond that there is no system: 7015 and 7016 are neighbours in the numbering, not necessarily in the colour.
RAL Design System plus is systematic, using hue, lightness and chroma, and like NCS it is built in the CIELab colour space. A conversion to RAL Design is therefore usually more accurate than one to RAL Classic.
Why conversion is never exact
The two collections were established independently. A colour from one does not reappear in the other, except by accident. A conversion therefore always looks for the nearest neighbour, and sometimes that neighbour is far away — particularly for saturated colours and for RAL Classic, a collection of only 216 colours.
On top of that, gloss level and substrate change perception. The same formulation reads differently in matt and in high gloss, because gloss changes how much ambient light is reflected. A conversion that is correct on paper can still look wrong on site.
And colour on a screen is always indicative. Only a physical sample is binding — that holds just as firmly for NCS as for RAL.
How to go about it
Establish the NCS code
If the code is in a specification or an order, you already have it. For existing work, measure it — judging a colour against a fan deck by eye gives too much spread.
Convert through the measured values
Translate the NCS code into CIELab and find the RAL colour with the smallest distance. Do not do this by eye, and not with a table of unknown origin.
Read the ΔE, not just the answer
A converter always returns something. Whether that answer is usable is what the ΔE tells you. Above ΔE 3 the choice should be made deliberately and recorded, not adopted in silence.
Check against a physical sample
Place the NCS sample and the RAL sample side by side, under the light the work will actually sit in. This is the step most often skipped and the one that most often costs money.
Convert it yourself
The colour converter of the Dutch Colour Institute calculates between NCS, RAL and other collections on the basis of measured values, and shows the ΔE for every result. It sits on the institute’s website and is free to use.
Go to the colour converter on snki.nlThe converter works from the NCS formula and does not rely on a copied colour list. That is deliberate: the NCS reference list is covered by database right, the calculation method is not.
What you measure and verify with
A conversion is only finished once you have seen it physically. That takes reference material:
Frequently asked questions
Is there an official conversion table from NCS to RAL?
No. NCS and RAL are independently defined collections, and neither organisation issues an official equivalence. Every conversion is a calculated approximation, with a deviation you can express as a ΔE.
What is an acceptable ΔE for a conversion?
Below ΔE 1 the difference is invisible to almost everyone. Between ΔE 1 and 3, trained eyes see it side by side but usually not in isolation. Above ΔE 3 it is a visibly different colour, and the choice should be recorded explicitly.
Should I convert to RAL Classic or to RAL Design?
To RAL Design, where that is allowed. It is built systematically in the same colour space as NCS and holds 1825 colours, so the nearest neighbour is usually closer. RAL Classic has only 216 colours, which makes the deviation larger.
Why does my conversion differ from a paint supplier’s?
Because there is no fixed table. Different parties use different measured values, different illuminants and sometimes a legacy table of their own. Always ask which measurement and which ΔE a figure is based on.
Do I need to specify the gloss level separately?
Yes. Colour and gloss are two properties. The same colour code reads differently in matt than in high gloss, so a specification naming only a colour code leaves room for variation in execution.