Use the Surface Finish Converter & Chart
Convert surface roughness between Ra µm, Ra µin, RMS and ISO N grades (N1–N12), estimate Rz, and look up typical Ra for machining, grinding.
- Free to use
- No signup
- Nothing to install
- Runs in your browser
Illustration. Open the tool for the real thing.
What is the Surface Finish Converter & Chart?
Surface roughness is quoted in different ways depending on where the drawing comes from: Ra in micrometres on metric drawings, Ra or RMS in microinches on US drawings, ISO N grades on older European ones, and Rz for peak-to-valley height. This converter takes any of Ra µm, Ra µin, RMS µin or an N grade (1–12) and shows all the others — Ra in both units, the nearest ISO grade, the RMS equivalent (about 1.11 × Ra), an Rz range (typically 4–7 × Ra) and a plain-language description of the finish — with one-click chips for common values like 0.8 µm, 1.6 µm, 3.2 µm, 63 µin and N7.
Two further tabs give typical roughness ranges by manufacturing process, from lapping and honing to grinding, turning, milling, die casting, sand casting, waterjet and laser cutting, SLA, SLS, DMLS and FDM printing, shown as a range on a logarithmic scale, and typical requirements by application — static and dynamic seals, bearing seats, hydraulic bores, gear flanks, press fits, cosmetic surfaces and food-contact parts. Figures are typical handbook ranges, not guarantees.
3 steps to your result
Open the tool and follow along. Nothing to install.
What you get
Instant conversion with the nearest ISO grade and an Rz range.
Typical Ra for 24 processes including 3D printing, on a log scale.
Typical Ra for seals, bearings, cosmetic and hygienic surfaces.
N1–N12 with µm and µin and typical processes.
AZRS tools are free to open and use.
It opens in your browser, so there is nothing to download.
Used for
Pick one to see how it fits.
How it compares
A plain look at this tool next to the usual alternative.
| This engineering calculator | Desktop software | |
|---|---|---|
| Install | Nothing to install | Usually an app or program to install |
| Account | No signup | Depends on the product |
| Cost | Free to use | Free or paid, depends on the product |
| Where it runs | In your browser tab | On your computer |
Questions people ask
What is Ra?
The arithmetic mean roughness — the average height deviation from the mean line.
Is Rz exactly 5 × Ra?
No, it varies by process; the range shown is a rule of thumb.
What is the N grade?
An ISO scale of roughness classes N1–N12 defined by Ra values.
Is it free?
Yes.
How do I use the Surface Finish Converter & Chart?
1. Enter a value and choose its unit. 2. Read the equivalents and the description. 3. Open the process tab to see what a method can achieve. 4. Open the application tab to choose a finish for your part.
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Try the Surface Finish Converter & Chart now
Convert Ra, µin, RMS and ISO N grades, with typical roughness by process and by. Free to use.
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