Metric and imperial conversions people actually need
A short reference for the four everyday conversions on financecalc — with the exact factors and when to round.
Travel, recipes, fitness trackers, and school problems still mix metric and imperial units. Using a consistent factor — and rounding only at the end — avoids compounding error. Below are the definitions our converters use, with practical notes unique to each pair.
Length: inches and centimeters
By international agreement, 1 inch = 2.54 centimeters exactly. Convert with multiply or divide; there is no offset. Height on forms is often given in feet and inches — convert total inches to centimeters in one step (for example, 70 inches × 2.54 = 177.8 cm).
Use the inches ↔ centimeters calculator when you need a quick bidirectional check. Round to one decimal for clothing and many product specs; keep more digits for engineering drawings until the final dimension callout.
Mass: pounds and kilograms
The international avoirdupois pound is 1 lb = 0.45359237 kg exactly. Bathroom scales and shipping labels often show one decimal place; airline baggage rules may state limits in either unit. Convert with the factor above, then round to the precision the rule requires.
Note: UK “stone” (14 lb) and troy pounds for precious metals are different systems. Our pounds ↔ kilograms converter is for avoirdupois body and cargo weight, not troy ounces.
Distance: miles and kilometers
The international mile is 1 mile = 1.609344 km exactly. Road signs, race distances (5K, 10K, half marathon), and car odometers are the usual use cases. A nautical mile (~1.852 km) is different and is used in aviation and marine navigation — do not use the road-mile factor for nautical charts.
Speed conversion uses the same factor when time is fixed (60 mph ≈ 96.56 km/h). Try the miles ↔ kilometers calculator for race and trip planning.
Temperature: Fahrenheit and Celsius
Temperature needs an offset as well as a scale factor:
- °C = (°F − 32) × 5/9
- °F = °C × 9/5 + 32
Water freezes at 0°C / 32°F and boils at 100°C / 212°F at standard pressure. Oven recipes and weather apps are the usual mix-ups; converting before you set a thermostat or bake temperature prevents large errors. Use the Fahrenheit ↔ Celsius converter for linked fields.
Rounding without lying to yourself
- Convert with full precision first.
- Round once for display or for a form field.
- Do not convert a rounded result back and forth repeatedly — error grows.
Bottom line
Exact definitions make length, mass, and distance conversions simple multiplications. Temperature needs the 32°F offset. Know which mile you mean, and round only when you present the answer. These notes are educational; for legal metrology or lab work, follow the standard your jurisdiction requires.