Result in Micrometres
0
Equivalent length value
Accurate SI metric length conversion for millimetres, micrometres (microns), nanometres, centimetres, metres, and inches
Convert millimetres to micrometres instantly using the exact factor of 1,000 µm per millimetre. Includes bidirectional conversion and a complete length unit breakdown for engineering, manufacturing, optics, and scientific precision measurement in 2026.
Professional SI metric length conversion for CNC machining tolerances, optical coatings, semiconductor fabrication, material thickness measurements, biology, medical device manufacturing, and all precision engineering applications requiring accurate mm and µm measurements
Convert millimetres to micrometres with full precision using the exact SI definition: 1 millimetre = exactly 1,000 micrometres. Since the SI metre is the base unit, all metric prefix conversions are exact powers of 10 — 1 mm = 10⁻³ m and 1 µm = 10⁻⁶ m, therefore 1 mm = 10⁻³ / 10⁻⁶ = 10³ = 1,000 µm exactly. Our tool delivers reliable results for any length from nanometre-scale measurements to multi-millimetre dimensions, with six simultaneous unit outputs per conversion.
Switch seamlessly between millimetres to micrometres and micrometres to millimetres conversion modes with one click. Get instant results in six length units simultaneously — micrometres (µm), millimetres (mm), nanometres (nm), centimetres (cm), metres (m), and inches (in) — from a single input value. The complete multi-unit breakdown is displayed with every result, giving engineers, scientists, machinists, and technicians a full precision-length reference panel in a single step.
Essential for CNC machinists working with tolerance specifications in both mm and µm, optical engineers specifying coating thicknesses and wavelength-scale features, semiconductor and PCB designers specifying trace widths and feature sizes down to sub-micron levels, medical device manufacturers specifying catheter wall thicknesses and implant surface finishes, materials scientists measuring film deposition thicknesses, and quality control engineers converting surface roughness measurements between Ra (µm) and equivalent mm values in inspection documentation.
Select conversion direction and enter your length value below
The millimetre (mm) is an SI unit of length equal to one thousandth of a metre (10⁻³ m). The micrometre (µm) — also called the micron — is an SI unit of length equal to one millionth of a metre (10⁻⁶ m). Since both are decimal subdivisions of the metre, converting between them is a simple power-of-ten shift: 1 mm = 1,000 µm and 1 µm = 0.001 mm. These are exact relationships requiring no approximation — the conversion factor 1,000 is an exact integer derived directly from the SI prefix system (milli = 10⁻³, micro = 10⁻⁶, ratio = 10³ = 1,000). There is no rounding, no uncertainty, and no approximation involved in any mm↔µm conversion.
In engineering practice, millimetres are used for visible-scale dimensions — component sizes, thread pitches, sheet metal thicknesses, pipe diameters, and mechanical drawings — while micrometres are used for precision-scale specifications — machining tolerances (e.g., ±5 µm = ±0.005 mm), surface roughness (Ra in µm), film coating thicknesses, optical wavelength-scale features, semiconductor node sizes, and biological cell dimensions. A typical human hair is 50–100 µm (0.05–0.10 mm) in diameter. A sheet of standard printer paper is approximately 100 µm (0.1 mm) thick. Machining tolerances for precision parts range from 1–50 µm (0.001–0.050 mm). Red light has a wavelength of approximately 0.65 µm (0.00065 mm = 650 nm).
Example: 2.5 mm × 1,000 = 2,500 µm | 500 µm ÷ 1,000 = 0.5 mm | 1 mm = 1,000 µm = 1,000,000 nm = 0.1 cm = 0.001 m = 0.039370 in
SI metric length scale: 1 m = 1,000 mm = 1,000,000 µm = 10⁹ nm. Key anchors: human hair = 50–100 µm; printer paper = 100 µm; red light wavelength = 0.65 µm = 650 nm; silicon transistor node (2026) ≈ 2–3 nm = 0.002–0.003 µm. CNC machining tolerances: ±5 µm = ±0.005 mm (precision); ±25 µm = ±0.025 mm (standard).
Complete reference table covering common millimetre values with their exact micrometre, nanometre, centimetre, metre, and inch equivalents. All µm values use the exact factor: 1 mm = 1,000 µm.
| Millimetres (mm) | Micrometres (µm) | Nanometres (nm) | Centimetres (cm) | Inches (in) | Notable Reference |
|---|---|---|---|---|---|
| 0.001 mm | 1 µm | 1,000 nm | 0.0001 cm | 0.0000394 in | 1 micron — precision limit |
| 0.005 mm | 5 µm | 5,000 nm | 0.0005 cm | 0.000197 in | Precision machining tolerance |
| 0.010 mm | 10 µm | 10,000 nm | 0.0010 cm | 0.000394 in | Fine machining tolerance |
| 0.025 mm | 25 µm | 25,000 nm | 0.0025 cm | 0.000984 in | Standard CNC tolerance (±0.025 mm) |
| 0.050 mm | 50 µm | 50,000 nm | 0.0050 cm | 0.001969 in | Human hair (fine) diameter |
| 0.100 mm | 100 µm | 100,000 nm | 0.0100 cm | 0.003937 in | Printer paper thickness |
| 0.200 mm | 200 µm | 200,000 nm | 0.0200 cm | 0.007874 in | Thin card stock |
| 0.500 mm | 500 µm | 500,000 nm | 0.0500 cm | 0.019685 in | 0.5 mm mechanical pencil lead |
| 1.000 mm | 1,000 µm | 1,000,000 nm | 0.1000 cm | 0.039370 in | 1 mm — standard reference |
| 2.000 mm | 2,000 µm | 2,000,000 nm | 0.2000 cm | 0.078740 in | 2 mm thread pitch (M2 bolt) |
| 5.000 mm | 5,000 µm | 5,000,000 nm | 0.5000 cm | 0.196850 in | 5 mm — common engineering dimension |
| 10.000 mm | 10,000 µm | 10,000,000 nm | 1.0000 cm | 0.393701 in | 1 cm = 10 mm |
| 25.400 mm | 25,400 µm | 25,400,000 nm | 2.5400 cm | 1.000000 in | Exactly 1 inch |
| 100.00 mm | 100,000 µm | 100,000,000 nm | 10.000 cm | 3.93701 in | 10 cm = 100 mm |
| 1,000.0 mm | 1,000,000 µm | 1,000,000,000 nm | 100.00 cm | 39.3701 in | 1 metre = 1,000 mm |
A micrometre (symbol: µm, from Greek "mikros" = small + "metron" = measure) is an SI unit of length equal to one millionth of a metre (10⁻⁶ m) or one thousandth of a millimetre (10⁻³ mm). It is also called a micron in everyday engineering language. The micrometre sits between the millimetre and nanometre in the SI scale: 1 mm = 1,000 µm; 1 µm = 1,000 nm. The symbol µ uses the Greek letter mu — in technical documents where µ cannot be typed, "um" is used as the ASCII substitute (e.g., "10um" = 10 µm). Do not confuse µm (micrometre) with mm (millimetre) — they differ by a factor of 1,000.
Engineering drawings specify dimensional tolerances in both mm and µm depending on the precision class required. ISO tolerance grades (IT grades) for machining: IT01 = 0.3–0.8 µm (0.0003–0.0008 mm, ultra-precision); IT1 = 0.8–1.5 µm; IT5 = 4–11 µm (precision engineering); IT7 = 10–25 µm (general purpose); IT11 = 60–160 µm (coarse). Standard CNC milling achieves ±25 µm (±0.025 mm); precision CNC grinding achieves ±1–5 µm (±0.001–0.005 mm). Surface roughness Ra (average roughness) is specified in µm: ground surfaces 0.4–1.6 µm; turned surfaces 1.6–6.3 µm; milled surfaces 1.6–12.5 µm. Converting Ra from µm to mm: divide by 1,000.
In optics, the micrometre scale is critical because it spans visible and infrared light wavelengths. Visible light: 0.380–0.700 µm (380–700 nm). Near-infrared: 0.700–2.5 µm. Mid-infrared: 2.5–25 µm. Anti-reflection coatings are typically 0.1–0.25 µm thick (100–250 nm = 0.0001–0.00025 mm). Optical fibre core diameters: single-mode 8–10 µm = 0.008–0.010 mm; multimode 50–62.5 µm = 0.050–0.0625 mm. Laser beam spot sizes: 1–100 µm = 0.001–0.100 mm. Diffraction grating line spacings: 0.5–10 µm = 0.0005–0.010 mm. All of these require routine mm↔µm conversion when working between optical component datasheets (µm) and mechanical engineering drawings (mm).
The micrometre scale covers the entire range of single-cell biology. Human red blood cell diameter: 6–8 µm (0.006–0.008 mm). White blood cell (lymphocyte): 7–15 µm. Platelet: 2–4 µm. Bacterium (E. coli): 1–2 µm long × 0.5 µm wide. Mitochondrion: 1–10 µm. Human hair cross-section: 50–100 µm (0.05–0.10 mm). Surgical suture diameters: 10–0 suture = 20 µm = 0.020 mm (finest); 2–0 suture = 330 µm = 0.330 mm. Catheter wall thicknesses: 100–500 µm = 0.1–0.5 mm. Drug particle sizes in inhalers: 1–5 µm = 0.001–0.005 mm (required to reach the lungs). Histology section thickness: 4–10 µm = 0.004–0.010 mm. These measurements require constant mm↔µm conversion in medical device documentation and clinical specifications.
Semiconductor fabrication uses the micrometre and nanometre scales. DRAM memory cell: ~50 nm = 0.05 µm = 0.00005 mm. Modern CPU transistor gate: 2–3 nm = 0.002–0.003 µm = 0.000002–0.000003 mm. Silicon wafer thickness: 725–775 µm = 0.725–0.775 mm. Printed circuit board (PCB) trace widths: minimum 50 µm = 0.05 mm (standard); 10–25 µm = 0.010–0.025 mm (HDI/fine pitch). PCB copper thickness: 35 µm = 0.035 mm (1 oz copper); 70 µm = 0.070 mm (2 oz). Solder mask thickness: 15–30 µm = 0.015–0.030 mm. Flip-chip bump pitch: 100–200 µm = 0.1–0.2 mm. Every PCB design file bridges mm (mechanical dimensions) and µm (trace/via specifications) — making this converter essential for electronics engineers daily.
The complete SI metric length hierarchy relevant to engineering: 1 km = 1,000 m. 1 m = 100 cm = 1,000 mm. 1 mm = 0.1 cm = 1,000 µm. 1 µm = 1,000 nm = 0.001 mm. 1 nm = 1,000 pm = 0.001 µm. 1 Å (ångström) = 0.1 nm = 0.0001 µm. All SI metric conversions are exact powers of ten — there are no approximation errors. Key cross-system bridges: 1 inch = 25.4 mm = 25,400 µm (exact); 1 thou/mil = 0.0254 mm = 25.4 µm (exact); 1 foot = 304.8 mm = 304,800 µm (exact). The "thou" or "mil" (1/1000 inch = 25.4 µm) is the imperial equivalent of the micrometre used in US manufacturing.
Converting mm to µm is simply multiplying by 1,000 — move the decimal point three places to the right. Examples: 0.025 mm → 25 µm; 0.1 mm → 100 µm; 1.5 mm → 1,500 µm; 10 mm → 10,000 µm. Converting µm to mm is dividing by 1,000 — move the decimal point three places to the left. Examples: 250 µm → 0.250 mm; 1,000 µm → 1.000 mm; 50 µm → 0.050 mm. Quick check: if your µm value seems oddly large or small, verify by asking: "is this value × 1,000 the mm value?" Example: 500 µm ÷ 1,000 = 0.5 mm — a 0.5 mm thickness is reasonable for thin sheet metal, confirming the conversion is correct.
Common engineering drawing tolerances converted between mm and µm: ±0.001 mm = ±1 µm (ultra-precision, grinding). ±0.002 mm = ±2 µm. ±0.005 mm = ±5 µm (precision CNC). ±0.010 mm = ±10 µm. ±0.020 mm = ±20 µm. ±0.025 mm = ±25 µm (standard CNC). ±0.050 mm = ±50 µm. ±0.100 mm = ±100 µm (general machining). ±0.200 mm = ±200 µm. ±0.500 mm = ±500 µm (coarse). ±1.000 mm = ±1,000 µm. These are the standard ISO and ASME tolerance bands referenced daily on engineering drawings, CMM inspection reports, and machining job cards across manufacturing industries worldwide.
Confusing micrometres (µm) and millimetres (mm) creates a 1,000-fold dimensional error — one of the most dangerous mistakes in precision engineering. A tolerance specified as "±25 mm" instead of "±25 µm" is 1,000 times looser — accepting parts that are 50 mm out of spec. A coating specified as "2 mm thick" instead of "2 µm" would be 2,000 times thicker than intended. Common contexts where µm/mm confusion occurs: surface roughness Ra values (always in µm — a Ra of 1.6 is 1.6 µm, not 1.6 mm); wavelength specifications in optics (always in µm or nm — never mm); semiconductor node sizes (always in nm or µm); and imported CAD drawings where the unit metadata may be misconfigured. Always double-check unit headers on technical drawings and inspection reports — and use this converter to sanity-check any unexpectedly large or small dimensional value.
Converting millimetres to micrometres requires multiplying by exactly 1,000. Here is the complete step-by-step process with a worked example:
For converting micrometres to millimetres, divide by 1,000 (or multiply by 0.001). Example: 250 µm ÷ 1,000 = 0.250 mm. Example: 25,400 µm ÷ 1,000 = 25.400 mm = exactly 1 inch. The bidirectional calculator above handles both directions instantly with full six-unit output. For related tools, our Millimetres to Centimetres Converter and Millimetres to Inches Converter cover the full metric and imperial length toolkit.
The Bureau International des Poids et Mesures (BIPM) is the international authority for the SI unit system, defining the metre as the base unit of length from which all metric prefixes — including milli (10⁻³) and micro (10⁻⁶) — are derived. The BIPM SI Brochure 9th edition confirms all SI prefix definitions and unit symbols, including µm (micrometre) and mm (millimetre). The exact 1 mm = 1,000 µm conversion is a direct consequence of these exact SI prefix definitions with no uncertainty.
Visit BIPM →Explore our full library of free conversion tools covering length, volume, weight, area, pressure, temperature, and energy — all built for fast, accurate results on any device. Every converter outputs complete multi-unit breakdowns in a single result panel, making them ideal for engineers, machinists, scientists, medical professionals, and students working across metric, imperial, and scientific measurement systems in professional and academic applications.
Browse All Converters →Our Millimetres to Inches converter is the essential companion for cross-system engineering work — converting the critical bridge between metric mm and imperial inches using the exact definition 1 inch = 25.4 mm = 25,400 µm. Includes thou/mil conversions (1 thou = 25.4 µm) for US manufacturing tolerance specifications, making it indispensable for engineers working between metric and inch-based drawings, imported components, and US-spec machinery dimensions in a metric engineering environment.
Convert mm to Inches →