Reference · Metrology

Unit conversion calculator

Convert engineering quantities across 40+ categories — length, pressure, torque, electrical, and more. Enter a value, pick units, and read the result instantly.

Unit category
Choose a quantity type, then set from and to units below.
input
output

Result

Length

Meter → Centimeter

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Pick a category, enter a value, and the result updates as you type.

About unit conversions

Ancient measurements

Early units were tied to the body and everyday objects before international standards existed.

  • Cubit — elbow to fingertip (Ancient Egypt)
  • Foot — human foot length (Rome)
  • Barleycorn — three grains of barley (Medieval England)
  • Hand — palm width (still used for horses)

Path to standardization

  • 1791 — metric system proposed in France
  • 1875 — Metre Convention signed by 17 nations
  • 1960 — SI system established
  • 1999 — Mars Climate Orbiter lost to a unit mix-up

Where conversions matter

  • Aerospace — altitude, speed, fuel mass
  • Civil — structural loads and material properties
  • Electrical — power, current, resistance
  • Chemical — concentration and flow rates
  • Mechanical — torque, pressure, temperature

Best practices

  • Verify units at every calculation step
  • Document unit conventions in project specs
  • Stay in one system within a single derivation
  • Include unit checks in design reviews
  • Trace results back to SI where possible
  • Mars Climate Orbiter (1999) — $125M loss from pound-force vs newton confusion
  • Gimli Glider (1983) — fuel calculated in pounds, loaded in kilograms
  • Vasa (1628) — inconsistent rulers across shipwright teams
  • Use automated conversion with documented factors
  • Independent double-check on critical quantities
  • Standardize units inside each organization
  • Train teams on dimensional analysis

Engineering insight

Unit errors scale with project complexity. Dimensional analysis catches mistakes that arithmetic alone will miss — always carry units through your working.

  • A light-year is roughly 9.46 × 10¹² km
  • One horsepower came from Watt's pony-lifting trials
  • The metric system nearly decimalized time too
  • Three countries still avoid metric officially: US, Myanmar, Liberia
  • The UK mixes imperial and metric daily
  • NASA now mandates SI after the Mars orbiter incident
  • Planck units derive from physical constants
  • The second is defined by atomic clocks
  • The metre has been tied to c since 1983
Frequently Asked Questions

Worked example: Convert 150 MPa to psi

  1. 1 MPa ≈ 145.038 psi
  2. 150 × 145.038

≈ 21,756 psi

How accurate are the unit conversions?

Conversions use standard SI and imperial definitions. Results are suitable for engineering calculations; for metrology-grade work, verify against your calibration standards.

Can I convert compound units?

This tool converts within common engineering categories: length, force, pressure, torque, and more. Select the quantity type and enter the value to convert.

What is the difference between US and UK gallons?

A US gallon is 3.785 L; an imperial (UK) gallon is 4.546 L. Always confirm which standard your datasheet uses.