Free Engineering Tool
Length Unit Converter
Convert between all major length units instantly. Metric and imperial units shown simultaneously.
All Units
| Unit | = Meters | Notes |
|---|---|---|
| 1 nm | 1×10⁻⁹ m | Nanometer |
| 1 μm | 1×10⁻⁶ m | Micrometer (micron) |
| 1 mil | 2.54×10⁻⁵ m | Thousandth of an inch |
| 1 mm | 0.001 m | Millimeter |
| 1 cm | 0.01 m | Centimeter |
| 1 inch | 0.0254 m | International inch |
| 1 foot | 0.3048 m | 12 inches |
| 1 yard | 0.9144 m | 3 feet |
| 1 m | 1 m | SI base unit |
| 1 km | 1000 m | Kilometer |
| 1 mile | 1609.344 m | Statute mile |
Common Engineering Conversions
| From → To | Multiply by | Example |
|---|---|---|
| mm → inch | 0.03937 | 25.4 mm = 1 inch |
| inch → mm | 25.4 | 1 inch = 25.4 mm |
| m → feet | 3.28084 | 1 m = 3.281 ft |
| feet → m | 0.3048 | 1 ft = 0.3048 m |
| km → miles | 0.62137 | 1 km = 0.621 mi |
| miles → km | 1.60934 | 1 mi = 1.609 km |
| μm → mil | 0.03937 | 25.4 μm = 1 mil |
| mil → μm | 25.4 | 1 mil = 25.4 μm |
Handy Memorization Tips
- 1 inch = 25.4 mm (exact, by international agreement since 1959)
- 1 foot = 12 inches = 304.8 mm
- 1 meter ≈ 39.37 inches ≈ 3 ft 3⅜ in
- 1 mile ≈ 1.6 km (for quick estimation: divide km by 8, multiply by 5)
- 1 mil (thou) = 0.001 inch = 25.4 μm (used for paint/coating thickness and shim sizes)
- 1 micron (μm) = 0.001 mm (surface roughness, bearing clearances)
Application-Specific Units
- Surface roughness: Usually in μm (Ra) or μin (microinch)
- Bearing clearance: μm or mil (thou)
- Shaft alignment: mm or mil
- Pipe sizes: DN (mm) in metric, NPS (inches) in imperial
- Sheet metal: mm or gauge number
- Wire diameter: mm or AWG (American Wire Gauge)
- Vibration displacement: μm peak-to-peak or mil peak-to-peak
- Machining tolerances: μm or 0.001 mm, often expressed as IT grades (ISO 286)
Historical Note
The meter was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole. Since 1983, it is defined as the distance light travels in vacuum in 1/299,792,458 of a second, making it the most precisely defined SI base unit.
Nominal pipe sizes do not correspond directly to any measured dimension. This table cross-references the metric DN and imperial NPS designations along with actual outside diameters.
| DN (mm) | NPS (inch) | Actual OD (mm) | Actual OD (inch) |
|---|---|---|---|
| 6 | ⅛ | 10.3 | 0.405 |
| 8 | ¼ | 13.7 | 0.540 |
| 10 | ⅜ | 17.1 | 0.675 |
| 15 | ½ | 21.3 | 0.840 |
| 20 | ¾ | 26.7 | 1.050 |
| 25 | 1 | 33.4 | 1.315 |
| 32 | 1¼ | 42.2 | 1.660 |
| 40 | 1½ | 48.3 | 1.900 |
| 50 | 2 | 60.3 | 2.375 |
| 65 | 2½ | 73.0 | 2.875 |
| 80 | 3 | 88.9 | 3.500 |
| 100 | 4 | 114.3 | 4.500 |
| 150 | 6 | 168.3 | 6.625 |
| 200 | 8 | 219.1 | 8.625 |
| 250 | 10 | 273.0 | 10.750 |
| 300 | 12 | 323.9 | 12.750 |
Yes. Since 1959, the international inch has been defined as exactly 25.4 mm by international agreement between the US, UK, Canada, Australia, New Zealand, and South Africa. This makes all inch-based conversions exact, not approximate.
A mil (also called a "thou") is one thousandth of an inch: 1 mil = 0.001 in = 25.4 μm. A micron (micrometer) is one millionth of a meter: 1 μm = 0.001 mm. So 1 mil = 25.4 microns. Mils are common in US engineering for coatings, shims, and clearances. Microns are the ISO/metric equivalent.
Pipe sizes (DN and NPS) are nominal designations — they don't directly correspond to any measured dimension. DN 25 ≈ NPS 1", but the actual OD is 33.4 mm (1.315"). Use the Pipe Size Cross-Reference table above for accurate conversions.
Surface roughness (Ra) is typically expressed in micrometers (μm) in ISO standards, or microinches (μin) in US practice. Common finishes: ground = 0.4–1.6 μm (16–63 μin), turned = 1.6–6.3 μm (63–250 μin), as-cast = 6.3–25 μm (250–1000 μin).
Wire and sheet metal gauges are not linear conversions — each gauge system (AWG, SWG, BWG) has its own lookup table. For example, 14 AWG wire = 1.628 mm diameter, while 14 gauge sheet steel (USS) = 1.897 mm thickness. Always use a gauge-specific lookup table.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional engineering calculators and measurement instruments.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
