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What is Ra 50 microinches in micrometers?

Last updated 10 August 2026

There is no exact answer, because Ra 50 microinches is not a preferred number. The nearest rung is 63, which pairs with Ra 1.6 micrometers.

Somebody will hand you a 50 microinch requirement sooner or later, usually from a drawing that was written to a house standard rather than to ISO 4288. There is no partner for it on the ladder, and a converter that silently returns 1.27 has invented a number.

The right move is not a rounding decision made quietly by whoever is doing the conversion. Name the nearest rung, agree with the customer whether the requirement tightens to 32 or opens to 63, and record which, because moving a specification is a deviation from the drawing and it needs to exist in writing.

Worked

Given	Ra 50 microinches
On the preferred-number ladder	no, this is the nearest rung
Standard pair	Ra 1.6 micrometers

Ra values pair on the ISO 4288 and ASME B46.1 preferred-number series. They are not conversions of one another and dividing does not produce them.
50 microinch is not a preferred number. The nearest rung is 63, which pairs with 1.6. Decide with the customer whether the requirement tightens to the next rung down or opens to the next one up, and record which, because that is a deviation from the drawing.
Dividing would have given 1.270, which is not a value any finish specification uses.

Open this case in the calculator, and change the numbers.

Computed by ctrlPlanner. ISO 4288, ASME B46.1.