Convert Micrometers (Ra) to Microinches (Ra)
Instantly convert Micrometers (Ra) (μm) to Microinches (Ra) (μin) with our free online calculator.
Formula: μm to μin — multiply by 39.3701
Reference Table
| Micrometers (Ra) (μm) | Microinches (Ra) (μin) |
|---|---|
| 1 | 39.3701 |
| 5 | 196.85 |
| 10 | 393.701 |
| 25 | 984.252 |
| 50 | 1968.5 |
| 100 | 3937.01 |
How to Convert Micrometers (Ra) to Microinches (Ra)
Formula
To convert Micrometers (Ra) (μm) to Microinches (Ra) (μin): multiply by 39.3701
Step-by-Step
- Start with your value in Micrometers (Ra) (μm).
- Multiply by 39.3701 to perform the conversion.
- The result is your value expressed in Microinches (Ra) (μin).
Conversion Factor
1 μm = 39.3701 μin
Reverse Factor
1 μin = 0.0254 μm
Worked Example
Convert 25 Micrometers (Ra) to Microinches (Ra): 25 μm = 984.252 μin
About Micrometer (Ra) (μm)
The SI unit of surface roughness — most commonly reported as the arithmetic mean deviation Ra (formerly CLA — Center Line Average) per ISO 4287 / ISO 21920-2 (the 2021 revision that replaced ISO 4287) in micrometers (μm). μm Ra is the global manufacturing standard for specifying surface finish on engineering drawings per ISO 1302 (Geometrical product specification — surface texture indication) and the unified GD&T notation per ISO 1101. Typical achievable values per Machinery's Handbook and Sandvik Coromant cutting-tool data: sand-cast iron surface 12.5-25 μm Ra; rough-turned/milled with carbide tool 3.2-12.5 μm Ra; fine-turned/finish-milled 0.8-3.2 μm Ra; ground 0.2-1.6 μm Ra; honed 0.1-0.4 μm Ra; lapped 0.025-0.2 μm Ra; mirror-polished/superfinished <0.025 μm Ra (1 μin or less); silicon-wafer CMP polished <0.001 μm Ra (atomic-scale). Measurement instruments per ISO 25178 (areal-roughness) and ASME B46.1: stylus profilometers (Mitutoyo SJ-410, Taylor Hobson Form Talysurf, Mahr MarSurf XR20) for contact methods; optical confocal microscopes (Sensofar S-Neox, Zeiss Smartzoom) and white-light interferometers (Zygo NewView, Bruker ContourGT) for non-contact methods.
About Microinch (Ra) (μin)
An imperial surface-roughness unit equal to exactly 0.0254 μm (1 μin = 25.4 nm). Microinches (μin) Ra is the traditional US unit on machining drawings per ASME B46.1 (Surface Texture — Surface Roughness, Waviness and Lay) and US-edition Machinery's Handbook. Typical achievable values per ASME B46.1 surface-finish charts and US machining-shop practice: sand-cast iron 500-1,000 μin Ra; rough turned/milled 125-500 μin Ra; fine turned/finish milled 32-125 μin Ra; ground 8-63 μin Ra; honed 4-16 μin Ra; lapped 1-8 μin Ra; mirror-polished/superfinished 1-4 μin Ra or less; precision optical mirror surfaces <1 μin Ra; silicon-wafer surfaces (after CMP polish) <0.1 μin Ra. US production-machining drawings still routinely call out '63' or '125' (μin Ra) for general-purpose finish; '32' for sealing surfaces; '16' for bearing fits per ANSI/ASME B46.1 + the unified-screw-thread standard ANSI/ASME B1.1. Converting μin Ra to μm Ra (multiply by 0.0254, or divide by 39.37) is a routine step when US-designed parts are manufactured in metric-default shops overseas (Mexico maquiladoras, China contract manufacturers).
Quick Facts
- 1 Micrometer (Ra) equals 39.3701 Microinches (Ra)
- 1 Microinch (Ra) equals 0.0254 Micrometers (Ra)
- Micrometer (Ra) is a unit of surface roughness
- Microinch (Ra) is a unit of surface roughness
- This conversion is commonly used in machining, quality control, and tribology
- The Micrometer (Ra) belongs to the metric system
- The Microinch (Ra) belongs to the imperial system
Common Micrometer (Ra) to Microinch (Ra) Conversions
| Micrometers (Ra) (μm) | Microinches (Ra) (μin) |
|---|---|
| 0.01 | 0.393701 |
| 0.1 | 3.93701 |
| 0.25 | 9.84252 |
| 0.5 | 19.685 |
| 1 | 39.3701 |
| 2 | 78.7402 |
| 3 | 118.11 |
| 5 | 196.85 |
| 10 | 393.701 |
| 15 | 590.551 |
| 20 | 787.402 |
| 25 | 984.252 |
| 50 | 1968.5 |
| 75 | 2952.76 |
| 100 | 3937.01 |
| 250 | 9842.52 |
| 500 | 19685 |
| 1000 | 39370.1 |
| 5000 | 196850 |
| 10000 | 393701 |
Understanding Micrometers (Ra)
The Micrometer (Ra) (symbol: μm) is a unit of surface roughness. The SI unit of surface roughness — most commonly reported as the arithmetic mean deviation Ra (formerly CLA — Center Line Average) per ISO 4287 / ISO 21920-2 (the 2021 revision that replaced ISO 4287) in micrometers (μm). μm Ra is the global manufacturing standard for specifying surface finish on engineering drawings per ISO 1302 (Geometrical product specification — surface texture indication) and the unified GD&T notation per ISO 1101. Typical achievable values per Machinery's Handbook and Sandvik Coromant cutting-tool data: sand-cast iron surface 12.5-25 μm Ra; rough-turned/milled with carbide tool 3.2-12.5 μm Ra; fine-turned/finish-milled 0.8-3.2 μm Ra; ground 0.2-1.6 μm Ra; honed 0.1-0.4 μm Ra; lapped 0.025-0.2 μm Ra; mirror-polished/superfinished <0.025 μm Ra (1 μin or less); silicon-wafer CMP polished <0.001 μm Ra (atomic-scale). Measurement instruments per ISO 25178 (areal-roughness) and ASME B46.1: stylus profilometers (Mitutoyo SJ-410, Taylor Hobson Form Talysurf, Mahr MarSurf XR20) for contact methods; optical confocal microscopes (Sensofar S-Neox, Zeiss Smartzoom) and white-light interferometers (Zygo NewView, Bruker ContourGT) for non-contact methods.
It belongs to the metric measurement system.
Micrometers (Ra) are commonly used in machining, quality control, and tribology.
Understanding Microinches (Ra)
The Microinch (Ra) (symbol: μin) is a unit of surface roughness. An imperial surface-roughness unit equal to exactly 0.0254 μm (1 μin = 25.4 nm). Microinches (μin) Ra is the traditional US unit on machining drawings per ASME B46.1 (Surface Texture — Surface Roughness, Waviness and Lay) and US-edition Machinery's Handbook. Typical achievable values per ASME B46.1 surface-finish charts and US machining-shop practice: sand-cast iron 500-1,000 μin Ra; rough turned/milled 125-500 μin Ra; fine turned/finish milled 32-125 μin Ra; ground 8-63 μin Ra; honed 4-16 μin Ra; lapped 1-8 μin Ra; mirror-polished/superfinished 1-4 μin Ra or less; precision optical mirror surfaces <1 μin Ra; silicon-wafer surfaces (after CMP polish) <0.1 μin Ra. US production-machining drawings still routinely call out '63' or '125' (μin Ra) for general-purpose finish; '32' for sealing surfaces; '16' for bearing fits per ANSI/ASME B46.1 + the unified-screw-thread standard ANSI/ASME B1.1. Converting μin Ra to μm Ra (multiply by 0.0254, or divide by 39.37) is a routine step when US-designed parts are manufactured in metric-default shops overseas (Mexico maquiladoras, China contract manufacturers).
It belongs to the imperial measurement system.
Microinches (Ra) are commonly used in machining, quality control, and tribology.
Why Convert Micrometers (Ra) to Microinches (Ra)?
Converting between Micrometers (Ra) and Microinches (Ra) is a frequent requirement for engineers, scientists, and students working with surface roughness values. Different industries and regions favour different unit systems, so having a dependable conversion tool saves time and prevents errors in technical calculations. Whether you are verifying a specification sheet, cross-checking simulation results, or preparing a report for an international audience, accurate surface roughness conversion is essential.
Frequently Asked Questions
How do I convert Micrometers (Ra) to Microinches (Ra)?
The SI unit of surface roughness — most commonly reported as the arithmetic mean deviation Ra (formerly CLA — Center Line Average) per ISO 4287 / ISO 21920-2 (the 2021 revision that replaced ISO 4287) in micrometers (μm)... To convert Micrometers (Ra) to Microinches (Ra), multiply by 39.3701. For example, 25 μm equals 984.252 μin.
How many Microinches (Ra) are in 1 Micrometer (Ra)?
There are 39.3701 Microinches (Ra) in 1 Micrometer (Ra).
How many Micrometers (Ra) are in 1 Microinch (Ra)?
There are 0.0254 Micrometers (Ra) in 1 Microinch (Ra).
What is the formula for Micrometer (Ra) to Microinch (Ra) conversion?
The formula is: multiply by 39.3701. This means 1 μm = 39.3701 μin.
Is a Micrometer (Ra) bigger than a Microinch (Ra)?
No. One Micrometer (Ra) is smaller than one Microinch (Ra) because 1 μm equals 39.3701 μin, which is greater than 1.
When do you need to convert between Micrometers (Ra) and Microinches (Ra)?
An imperial surface-roughness unit equal to exactly 0. Micrometer (Ra) and Microinch (Ra) are both surface roughness units, so conversion comes up whenever one source of information uses one unit and another uses the other — a classic cross-reference challenge in engineering, trade, travel, and everyday life.