A unit conversion calculator answers the everyday questions people search millions of times per month: How many feet in a meter? What is 100 °C in Fahrenheit? How many pounds is 70 kg? How many gallons in a liter? This guide explains how conversions work, when to use metric vs imperial units, and how to get instant accurate answers with our free Conversion Calculator.
Convert now: Open the free Conversion Calculator — length, temperature, area, volume, and weight with instant results and a full equivalence table. No sign-up required.
What is a conversion calculator?
A conversion calculator converts a measurement from one unit to another within the same physical quantity — length to length, temperature to temperature, and so on. Unlike a basic four-function calculator, it knows the fixed ratios between units (for example, 1 inch = 2.54 cm exactly) and applies the correct formula, including offset scales like Celsius and Fahrenheit.
Most popular unit conversions (search intent)
These are among the highest-volume conversion searches worldwide. Use the matching tab on the Conversion Calculator:
| People search for… | Category | Quick answer |
|---|---|---|
| meters to feet / cm to inches / km to miles | Length | 1 m ≈ 3.281 ft; 1 in = 2.54 cm; 1 mi ≈ 1.609 km |
| Celsius to Fahrenheit / oven temperature | Temperature | F = (9/5)C + 32 — 100 °C = 212 °F (boiling water) |
| kg to lbs / grams to ounces | Weight | 1 kg ≈ 2.205 lb; 1 oz ≈ 28.35 g |
| liters to gallons / ml to cups | Volume | 1 US gal ≈ 3.785 L; check US vs imperial gallons for UK recipes |
| square feet to square meters / acres to hectares | Area | 1 sq ft ≈ 0.0929 sq m; 1 acre ≈ 0.405 hectare |
How to use the online conversion calculator
- Open the Conversion Calculator.
- Choose a tab: Length, Temperature, Area, Volume, or Weight.
- Type a number in From and select source and target units.
- Read the result and scroll the equivalence table for all units at once.
- Click the swap arrow to reverse units instantly.
Results update as you type — no page reload. Click Calculate then Save to store a conversion in your browser for later reference.
Conversion formulas explained
Linear units (length, area, volume, weight)
Most units scale by a constant factor relative to a base unit. To convert from unit A to unit B:
valueB = valueA × (factorA ÷ factorB)
Example: convert 5 kilometers to meters. Kilometer factor = 1000, meter factor = 1 → 5 × (1000 ÷ 1) = 5000 meters.
Temperature (offset scales)
Temperature does not start at zero on every scale, so you add or subtract offsets:
- Celsius to Fahrenheit: F = (9/5) × C + 32
- Fahrenheit to Celsius: C = (5/9) × (F − 32)
- Celsius to Kelvin: K = C + 273.15
Example: 25 °C → (9/5) × 25 + 32 = 77 °F (comfortable room temperature).
Metric system vs US customary / imperial
The International System of Units (SI) — meters, kilograms, liters, Celsius — is the global standard for science, medicine, and most countries’ road signs and packaging. The United States still uses feet, miles, pounds, and Fahrenheit in daily life, while the UK mixes metric with imperial pints and miles.
Practical tips:
- Travel: speed limits abroad are usually km/h; fuel may be priced per liter.
- Recipes: US cups and fluid ounces differ from UK imperial volumes — pick the right gallon type in the Volume tab.
- Real estate: US listings use square feet; many other markets use square meters.
- Fitness: gym weights may be in kg or lbs — convert before comparing to a BMI or training log.
Length conversion examples
- 1.75 m (typical door height) ≈ 5 ft 9 in
- 42.195 km (marathon) ≈ 26.2 miles
- 30 cm (ruler length) ≈ 11.8 inches
Weight and volume for shipping, cooking, and health
Airline baggage limits are often in kilograms internationally and pounds domestically. Nutrition labels may list grams while home scales show ounces. Baking forums switch between milliliters and cups — volume conversions prevent ruined recipes.
After converting weight units, you can plug metric height and weight into our BMI Calculator for body composition context. For discount math on imported goods priced in different currencies’ worth of units, pair conversions with the Percent Off Calculator or Percentage Calculator.
Common mistakes to avoid
- Confusing US and imperial gallons — a UK gallon is larger than a US gallon.
- Using area factors for length — square feet are not linear feet squared in mental math; use the Area tab.
- Rounding too early — convert first, then round for display.
- Treating °F and °C as proportional — doubling Celsius does not double Fahrenheit.
When to double-check conversions
Everyday cooking, homework, DIY, and travel are fine with a standard converter. Medical dosages, aviation fuel, structural engineering, and legal land surveys may require certified tools or official tables. This guide and calculator are educational — not a substitute for professional specifications.
Get accurate conversions in one click
Whether you need meters to feet for a furniture order, Celsius to Fahrenheit for an oven, liters to gallons for a road trip, or kg to lbs for luggage, the Conversion Calculator handles it with a clear result line and full equivalence table. Bookmark it for the next time a measurement does not match your ruler, recipe, or weather app.
Related calculators on ShoutingNow
- Conversion Calculator — meters to feet, C to F, liters to gallons, kg to lbs, and more
- Unit Conversion Calculator Guide — formulas, metric vs imperial, and worked examples
- Percentage Calculator — solve percent-of, is-what-percent, and change problems
- BMI Calculator — body mass index from height and weight (metric or imperial)
- Age Calculator — exact age in years, months, and days