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Reviewed by CalculatorApp.me Engineering & Science Team
SI, imperial, temperature, data storage — every unit and conversion factor explained.
7
SI base units
100+
Units supported in this converter
1875
Year of the Metre Convention
3 countries
Still not fully metric (USA, Liberia, Myanmar)
Convert between 100+ units across 12 categories including length, mass, temperature, area, volume, speed, time, data, pressure, energy, and more.
Meters to Feet
ft
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A unit converter applies dimensional analysis to transform a measurement expressed in one unit into its equivalent in another unit of the same physical quantity. Every conversion multiplies the value by a conversion factor — the ratio of the two units relative to a common base.
The International System of Units (SI) defines 7 base units (metre, kilogram, second, ampere, kelvin, mole, candela) from which all other units are derived. Imperial and US customary units remain common in everyday life in the USA, UK (partially), and a handful of other countries.
Unit conversion errors have had catastrophic consequences in history — including the loss of the NASA Mars Climate Orbiter ($327M) in 1999 due to a metric/imperial confusion between engineering teams.
°F to °C: C = (F − 32) × 5/9 °C to °F: F = (C × 9/5) + 32 °C to K: K = C + 273.15 K to °C: C = K − 273.15 Absolute zero: −273.15 °C = 0 K = −459.67 °F
Temperature is the only common conversion requiring both addition and multiplication (affine, not linear).
1 inch = 2.54 cm (exact) 1 foot = 30.48 cm (exact) 1 mile = 1.60934 km 1 yard = 0.9144 m (exact) 1 nautical mi = 1.852 km (exact) 1 lightyear = 9.461 × 10¹⁵ m
The inch and foot are now defined exactly via the metric system.
1 pound = 453.592 grams 1 ounce = 28.3495 grams 1 stone = 14 pounds = 6.35 kg 1 US ton = 2000 lbs = 907.185 kg 1 metric tonne = 1000 kg = 2204.6 lbs
'Weight' (force) and 'mass' differ in physics but are used interchangeably in everyday unit conversion.
| Quantity | SI Unit | Imperial / US | Conversion Factor | Notes |
|---|---|---|---|---|
| Length | metre (m) | inch / foot / mile | 1 m = 3.2808 ft | Defined via speed of light |
| Mass | kilogram (kg) | pound (lb) / ounce | 1 kg = 2.2046 lb | Defined via Planck constant (2019) |
| Temperature | kelvin (K) | Fahrenheit (°F) | See formula | Affine conversion (not pure multiplication) |
| Volume | litre (L) | gallon / fluid oz | 1 L = 0.2642 US gal | US and UK gallon differ (3.785 vs 4.546 L) |
| Speed | m/s |
Charlemagne decreed uniform weights and measures across the Holy Roman Empire — one of the first major attempts at measurement standardization.
The French Revolution produced the metric system — a rational, decimal-based framework. The metre was defined as 1/10,000,000 of the Earth's meridian quadrant.
17 nations signed the treaty establishing the International Bureau of Weights and Measures (BIPM), creating the first global measurement authority.
The 11th General Conference on Weights and Measures formalized the International System of Units (SI) with 6 base units (candela added in 1967).
A $327M spacecraft was lost because Lockheed Martin sent thrust data in pound-force seconds while NASA expected newton-seconds — a historical unit conversion failure.
BIPM / SI Brochure
Official SI definitions of all 7 base units, 22 derived units, and prefixes — the authoritative reference for all scientific measurement.
NIST
NIST SP 811 provides official US guidance on SI notation, conversion factors, and units for American scientists and engineers.
NASA / JPL
The official crash investigation report detailing the £327M failure caused by a pound-force vs. newton unit mismatch.
ISO 80000
ISO 80000 defines physical quantities and units for engineering applications — complementing SI with domain-specific notation.
The metric and imperial systems are completely incompatible.
They are fully interoperable — every imperial unit has an exact metric equivalent. The inch is defined as exactly 2.54 cm by international agreement.
1 kilogram = 1 pound.
1 kilogram ≈ 2.205 pounds. The kilogram is a unit of mass; the pound is technically a force unit in physics, though used as mass in everyday contexts.
°F and °C differ only by a simple multiplication factor.
Temperature conversion requires both multiplication and addition (affine transformation): °C = (°F − 32) × 5/9. You cannot simply multiply.
1 GB = 1,000 MB.
In binary (IEC) convention, 1 GiB = 1,024 MiB. Hard drive makers use SI (1 GB = 1,000 MB), which creates the apparent 'missing space' when you buy a 1TB drive.
Physics formulas, chemistry converters, engineering calculators — all in one place.
Browse Engineering Tools →Last updated:
1 KB = 1,024 bytes (IEC kibibyte) 1 MB = 1,048,576 bytes 1 GB = 1,073,741,824 bytes 1 TB = 1,099,511,627,776 bytes (SI: 1 KB = 1,000 bytes) Difference at 1 TB: ~73.7 GB
SI uses powers of 1,000 (kB, MB). IEC uses powers of 1,024 (KiB, MiB). Hard drive makers use SI; operating systems use IEC.
| mph / knots |
| 1 mph = 1.60934 km/h |
| Knots = nautical miles per hour |
| Area | m² | sq ft / acres | 1 m² = 10.7639 sq ft | 1 acre = 4,046.86 m² |
All 7 SI base units were redefined in terms of fundamental physical constants (Planck h, Boltzmann k, elementary charge e, etc.) — eliminating all physical artefacts.
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