Whether you are following a recipe, reading a spec, or traveling, here are the conversions you actually need — with mental shortcuts for each.
The foundation is exact: one inch equals exactly 2.54 centimeters. From there, one foot is 30.48 cm and one mile is 1.609 kilometers. A quick mental trick: to estimate kilometers in miles, multiply by 0.6 (100 km ≈ 62 miles). Convert precisely with the cm to inches converter, km to miles converter, or the all-purpose length converter.
One kilogram is about 2.205 pounds. The mental shortcut: double the kilograms and add 10% (50 kg → 100 + 10 = ~110 lbs). For exact figures use the kg to lbs converter, pounds to kg converter, or the full weight converter.
This one trips people up because it has both a scale and an offset. The formula is °F = °C × 9/5 + 32. A rough estimate: double the Celsius and add 30 (20°C → ~70°F). Remember that −40° is identical in both scales. Use the Celsius to Fahrenheit converter or full temperature converter for accuracy.
A US gallon is about 3.785 liters — and note the UK imperial gallon is larger at 4.546 liters, a frequent source of confusion. A US cup is about 237 ml, while metric cups are 250 ml, which matters in baking. Convert with the liters to gallons converter or volume converter.
To convert miles per hour to kilometers per hour, multiply by 1.609 (60 mph ≈ 97 km/h). For physics, divide km/h by 3.6 to get meters per second. The speed converter handles knots and m/s too.
Published 2026-01-22 · USFreeTools.com Editorial Team