Convert Nanometers to Micrometers (Ra)

The Nanometer (symbol: nm) is a unit of surface roughness. A surface-roughness unit equal to exactly 0.001 μm = 10⁻⁹ m. Nanometer-level roughness specification (typically reported as nm Rq RMS, not nm Ra) is required for: precision optical surfaces (mirrors for large-aperture telescopes per ESO E-ELT primary-mirror specification < 1 nm RMS over relevant spatial frequencies; EUV lithography photomask substrates for ASML scanners 0.2-0.5 nm RMS per SEMI P37 / P38 specifications), silicon wafer manufacturing (300 mm prime wafers achieve 0.1-0.3 nm Ra over the polished surface after CMP per SEMI M1 standard), and high-performance hydrodynamic / hydrostatic precision bearings (turbomolecular vacuum pump bearings, atomic-clock-grade reference flats). Atomic-Force Microscopy (AFM — Bruker Dimension Icon, Park Systems NX, Asylum MFP-3D) and white-light interferometry (Zygo, Bruker, Sensofar) resolve surface variations down to sub-nanometer (<0.1 nm RMS) over micrometer-scale fields. The IUPAC 2014 official roughness conversion convention recommends nm only when the underlying measurement instrument resolves <10 nm features — otherwise μm is preferred. Used heavily in EUV photomask qualification, optical-table flat-mirror specs, and semiconductor wafer-flatness GBIR/SFQR metrics.

It belongs to the metric measurement system.

Nanometers are commonly used in machining, quality control, and tribology.

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.