Imperial to Metric Conversion Calculator
Convert any imperial measurement to metric — choose from length, weight, volume, temperature, area, or speed and see all relevant metric equivalents for the same numeric value at once.
Measurement type
Primary metric equivalent
- 1
Conversion factor
2.541 inch = 2.54 cm (exact, by international definition since 1959). - 2
Centimetres
12 × 2.54 = 30.4800
How does this calculator work?
Key imperial-to-metric factors: 1 in = 2.54 cm, 1 ft = 0.3048 m, 1 mile = 1.609 km, 1 lb = 0.4536 kg, 1 US gal = 3.785 L, °C = (°F−32)×5/9. Select a category and enter your value to see all relevant metric equivalents instantly.
Formula
How this is calculated
The United States (and, informally, the UK for some purposes) uses customary/imperial units, while the rest of the world and all scientific work uses the International System of Units (SI/metric). Converting between them uses fixed, internationally agreed factors. Length: 1 inch = 2.54 cm exactly (since 1959 international agreement); 1 foot = 12 in = 30.48 cm; 1 mile = 1 609.344 m. Weight: 1 pound (avoirdupois) = 0.453 592 37 kg exactly; 1 ounce = 1/16 lb ≈ 28.35 g. Volume: 1 US gallon = 3.785 411 784 L — note that 1 UK/imperial gallon = 4.546 L (about 20% larger); this calculator uses US customary volume units. Temperature: °C = (°F − 32) × 5/9; Kelvin = °C + 273.15 (0 K is absolute zero).
The numeric value entered is applied to every row in the selected category simultaneously, so you can quickly compare: for example, "12" in the Length category shows 12 inches in cm, 12 feet in metres, 12 yards in metres, and 12 miles in km. This is useful when you have a number and are unsure which imperial unit applies — scan the results for the one that looks sensible.
All conversion factors are the exact NIST-defined values or derived from them. Results are shown to four or five decimal places; for everyday use, one or two decimal places are sufficient.
Frequently asked questions
No. 1 US gallon = 3.785 L, while 1 UK (imperial) gallon = 4.546 L — roughly 20% larger. This calculator uses US gallons. If you need UK gallons, read the "UK gallons → litres" row.
Since 1959, 1 international inch = 25.4 mm exactly, by international agreement between the US, UK, Canada, Australia, New Zealand, and South Africa. This makes 1 foot = 0.3048 m exactly and 1 mile = 1 609.344 m exactly.
The UK officially adopted metric in the 1970s but legally retained miles for road signs, pints for draught beer, and stones/pounds for body weight in common usage. Food labels, medicine, and most trade are fully metric.
Also known as
TG we-Calculate Editorial Team. (2026). Imperial to Metric Conversion Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/imperial-to-metric-conversion-calculator
TG we-Calculate Editorial Team. "Imperial to Metric Conversion Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/imperial-to-metric-conversion-calculator.
TG we-Calculate Editorial Team, "Imperial to Metric Conversion Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/imperial-to-metric-conversion-calculator
@misc{wecalculate_imperial_to_metric_conversion_calculator, title = {Imperial to Metric Conversion Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/imperial-to-metric-conversion-calculator}}, year = {2026}, note = {TG we-Calculate} }
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