Last updated 10 August 2026
Ra 63 microinches is Ra 1.6 micrometers.
Both values are entries on the preferred-number series defined by ISO 4288 and ASME B46.1. They are paired, not converted: each is a standard value in its own right, and the ladder is what makes them equivalent.
This particular pair is the reason a bad habit survives. 63 divided by 39.37 is 1.600, so the one value most people check by hand is the one where dividing appears to work. It stops working immediately either side of it, which is why the next question is worth reading.
| Given | Ra 63 microinches |
|---|---|
| On the preferred-number ladder | yes |
| Standard pair | Ra 1.6 micrometers |
Open this case in the calculator, and change the numbers.
Computed by ctrlPlanner. ISO 4288, ASME B46.1.
This converts one value. ctrlPlanner holds both units on the same plan and applies the same inward rounding everywhere, so a whole print comes out in whichever unit the customer asked for.
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