Last updated 10 August 2026
Ra 1.6 micrometers is Ra 63 microinches, and this is the one rung where multiplying by 39.37 happens to land on the standard value.
Going from metric to imperial is where the shortcut looks most convincing, because the metric ladder is the one written in round numbers. 1.6 times 39.37 is 63.0. So is nothing else: 3.2 gives 126, against a standard 125, and 0.4 gives 15.7, against a standard 16.
A metric drawing arriving at an imperial shop is also where a converted value does the most damage, because the shop has comparator blocks in microinches and will pick the nearest one anyway. Naming the rung on the traveler rather than the quotient means the value on paper is the value being checked against.
| Given | Ra 1.6 micrometers |
|---|---|
| On the preferred-number ladder | yes |
| Standard pair | Ra 63 microinchs |
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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