Unit converters · Length, mass, area, volume
Convert metric and inch-pound lengths
Every value goes through the meter, then to the target unit. The inch is 25.4 mm exactly since the 1959 agreement, as in the NIST SI conversion factors.
Calculate
How the calculator works
The math multiplies the input by the “to meter” factor, then divides by the target unit’s factor. No approximate table (“1 m ≈ 3.3 ft”) is used: the international foot is 0.3048 m exact, the yard 0.9144 m, the international mile 1,609.344 m. The display may show many decimals; the remaining limit is floating-point, visible mainly between millimeters and miles.
Formula and method
L(m) = x × kfrom ; y = L(m) / kto
k is the unit’s factor to the meter (BIPM / NIST SP 811, appendix B).
1 in = 25,4 mm = 0,0254 m
Exact identity, not a lab rounding.
The International System defines the meter. US customary units listed here are the international definitions (inch, foot, yard, mile) from the NIST guide, not the historical US survey foot. A nautical mile is not offered: it is not 1,609.344 m. Prefixes mm, cm, km are powers of ten of the meter.
Worked example
1.75 m to centimeters
x = 1.75, from m to cm.
- In meters: 1.75 m (already SI).
- To cm: 1.75 / 0.01 = 175 cm.
175 cm.
5 feet to meters
x = 5, from ft to m.
- 5 × 0.3048 = 1.524 m.
1.524 m exactly (international foot).
Input notes
- Value
- The numeric value alone, without the unit. The unit is chosen in From / To.
- From
- Unit of the typed quantity. Default is the meter.
- To
- Unit of the result. Default is the centimeter, a common SI everyday conversion.
Assumptions and limits
Assumptions
- Foot, yard, and mile are the international definitions, not local survey units.
- The mile is the international statute mile (1,609.344 m), not the nautical mile.
- Factors are exact; display may round for reading.
Limits
- No league, no fathom, no nautical mile.
- A mm → mi conversion accumulates floating-point noise beyond about the 10th displayed decimal.
- Machining tolerances (ISO fits) are not unit conversions.
How to read the result
1.75 m = 175 cm is not an approximation: it is the SI prefix. 5 ft = 1.524 m is equally exact with the international foot. If a US plan mixes inch fractions and meters, convert each dimension; do not add mixed units. For an area (m², acres), use the area converter: squaring a length is not done here.
Common mistakes
Confusing statute mile and nautical mile (1,852 m).
Here, mi = 1,609.344 m. The nautical mile is not in the list.
Taking 1 ft = 30 cm.
1 ft = 0.3048 m = 30.48 cm exactly, not 30 cm.
Converting an area with this tool (12 m “into m²”).
A length is not an area. Switch to the area converter.
Comparison
| Unit | To the meter | Note |
|---|---|---|
| mm, cm, m, km | 10⁻³, 10⁻², 1, 10³ | SI prefixes |
| in | 0.0254 | 25.4 mm exact |
| ft | 0.3048 | 12 inches |
| yd | 0.9144 | 3 feet |
| mi | 1,609.344 | International statute mile |
Related calculations
- Area converterFactors are SI areas and the international acre. A hectare is 10,000 m² exactly. The acre used here is not the arpent, nor a local survey acre.
- Volume converterThe liter is 1 dm³, or 0.001 m³ exactly. The US gallon and the UK imperial gallon are not the same capacity: the tool separates them, with no ambiguous “gallon” option.
- Weight (mass) converterEveryday speech says “weight”; SI speaks of mass. Conversion goes through the kilogram. The pound (lb) is 0.45359237 kg exactly, a NIST factor, not a weighing on Earth.
- Temperature converterCelsius and Fahrenheit are offset; you do not multiply a “degree” like a meter. Every conversion goes through kelvin. Below 0 K there is no thermodynamic temperature.
- Speed converterEvery speed routes through the metre per second. 1 km/h is exactly 1/3.6 m/s, and a knot is one nautical mile (1,852 m) per hour, not a statute mile.
- Angle converterEvery angle routes through the radian, the SI unit. A half turn is π radians, 180 degrees or 200 gradians: three ways of describing the same opening.
Frequently asked questions
Is the inch rounded to 25.4 mm?
No. 1 inch = 25.4 mm exactly, by definition (NIST / 1959 agreement).
Before 1959, the US and the Commonwealth did not share exactly the same inch. Since then, the international inch is 25.4 mm. The NIST SI conversion-factor guide repeats that identity. This converter does not “measure” a machined inch: it applies the legal factor.
Why go through the meter?
To have one factor table, and stay glued to SI definitions.
Converting inches → miles by chaining rounded tables accumulates error. Inches → meters → miles uses only exact factors. BIPM defines the meter; NIST publishes factors to common US units.
What about the US survey foot?
This tool uses the international foot (0.3048 m). The historical US survey foot is something else and is not offered.
US cadastral coordinates long used a slightly different survey foot. For everyday use (DIY, sport, cooking), the international foot is the right one. A US surveyor on an old survey must check the datum, not this converter.
How do I convert 1.5 km to miles?
1.5 × 1000 / 1,609.344 ≈ 0.932 miles.
Type 1.5, from km to mi. The internal result is exact up to the factor; the display shows several decimals. A road sign then rounds by local rule, which the tool does not do.
Author and update
Written by Rédaction HexaCalc (editorial team). Content last updated: August 25, 2026. No third-party medical or financial review is claimed.
- NIST Guide to the SI, Appendix B: Conversion Factors — National Institute of Standards and Technology
- The International System of Units (SI) — Bureau international des poids et mesures (BIPM)
Move on to an area
Hectares, acres, and m² convert with squared factors, not by “multiplying a length by itself” by hand without a unit.
Open the area converterCategory: Unit converters