Metric vs. Imperial
Which countries use which, and the minimum set of conversions for travellers and readers.
Almost every country uses metric officially. Three holdouts — US, Liberia, Myanmar — still use imperial as primary.
Almost the entire world uses metric. Three countries — the US, Liberia, and Myanmar — still use imperial officially, and the UK uses a mixture (metric for weight and length in most contexts, imperial for roads and beer).
Part of: Unit Conversion Tools
Quick answer
Almost every country uses metric officially. Three holdouts — US, Liberia, Myanmar — still use imperial as primary.
Key points
- ▸ Length: 1 inch = 2.54 cm. 1 ft ≈ 0.3 m. 1 mile ≈ 1.6 km.
- ▸ Weight: 1 lb ≈ 0.454 kg. 1 kg ≈ 2.2 lb. 1 stone = 14 lb = 6.35 kg.
- ▸ Volume: 1 US gal = 3.785 L. 1 UK gal = 4.546 L. 1 L ≈ 33.8 US fl oz.
- ▸ Temperature: °C = (°F − 32) × 5/9. Reference: 0°C = 32°F, 37°C = 98.6°F (body).
- ▸ UK quirk: weight in stone-and-pounds for people, kg for food. Height in feet-and-inches or cm.
Examples
- UK body weight"11 stone 3" = 11 × 14 + 3 = 157 lb = 71.2 kg.
- Recipe: 1 cup flourUS cup = 240 ml ≈ 125 g flour. UK recipes use grams directly — cups are an American convention.
- Temperature forecast75°F = 24°C (warm). 40°F = 4°C (cold). Use (F − 30) ÷ 2 for a quick approximation.
When to use which tool
- Length ConverterLength across systems — feet, inches, metres, miles, kilometres.Convert between meters, feet, inches, miles, kilometers, yards, and more.
- Weight ConverterWeight across pounds, kilograms, stones, ounces.Convert between kilograms, pounds, ounces, grams, stones, and tons.
- Volume ConverterVolume including the US vs. UK gallon distinction.Convert between liters, gallons, cubic meters, milliliters, cups, pints, and more.
- Temperature ConverterFahrenheit ↔ Celsius, with decimal precision for medical or scientific use.Convert between Celsius, Fahrenheit, Kelvin, and Rankine.
Related
- Length ConverterConvert between meters, feet, inches, miles, kilometers, yards, and more.
- Weight ConverterConvert between kilograms, pounds, ounces, grams, stones, and tons.
- Volume ConverterConvert between liters, gallons, cubic meters, milliliters, cups, pints, and more.
- Temperature ConverterConvert between Celsius, Fahrenheit, Kelvin, and Rankine.
- Common Length ConversionsThe conversion factors worth memorising, and mental-math shortcuts for the rest.
- Fahrenheit vs. CelsiusThe exact formula, and the quick approximation that gets you within 2°.
- Litres vs. GallonsOne litre, two different gallons — know which one you are dealing with.
Frequently asked questions
› Why does the UK use a mix? Troubleshooting
The UK officially went metric in the 1960s–70s but never fully switched consumer habits. Road signs, beer, and body weight stayed imperial; food, weather, and science went metric.
› Is metric always easier? Trust & accuracy
For arithmetic yes — everything scales by 10. But imperial units (foot, inch, pound) are often more human-sized for everyday measurements, which is part of why they persist.
› How accurate are online calculators and converters? Trust & accuracy
Online calculators are only as accurate as the numbers, units, assumptions, and rounding choices you enter. Recheck the input values first, then compare the formula against your real situation. For legal, tax, medical, financial, or professional decisions, treat the result as a planning estimate, not advice.
› What inputs should I double-check first? Troubleshooting
Double-check units, dates, percentages, decimal placement, and whether the input is before-tax, after-tax, gross, net, original, or final. Most calculator mistakes come from feeding the right formula the wrong base. If the result feels off, rebuild it from a simple worked example.
› Why do two calculators sometimes give different answers? Comparison
Two calculators may round at different steps, use different defaults, or interpret the same label differently. Percent, time, finance, and unit tools are especially sensitive to basis and rounding rules. Compare the formula, not just the final number, before deciding which result to trust.