Sandpaper grit converter
Convert grit numbers between European P-grades, US CAMI, Japanese JIS water stones and the average particle size in micrometers.
That's about the same as P120 paper for bare wood.
What it means
How coarse is that grit?
Average particle sizes from FEPA (ISO 6344), ANSI B74.12/B74.18 and JIS R6001. Brands and bonds vary; treat values between listed grits as estimates.
Every unit
That grit in every standard
Learn
Three things worth knowing
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Skip no more than one grit
Go 80 → 120 → 180 → 240 rather than 80 → 240: each paper should only remove the scratches of the one before.
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Sieves per inch
Grit numbers began as sieve meshes: grit 60 passed a screen with 60 wires per inch. Finer powders were graded by settling in water, so the numbers kept going where sieves could not.
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P1500 is not 1500
Above 220, a P number is coarser than the same CAMI number and much coarser than the same JIS number: JIS #1000 is about 12 µm, P1000 18 µm.
Shortcuts
Popular grit conversions
Background
About grit numbers
A grit number started as the number of openings per inch of the sieve the abrasive passed through: the higher the number, the finer the grit. Today each standard publishes its own table of average particle sizes.
Up to about 220 the European P scale and the US CAMI scale agree closely. Beyond that they drift apart: a P1000 paper (18 µm) is about as fine as CAMI 600, and a 1000 grit Japanese water stone is finer still.