Convert Any Unit in Seconds
Kilometers to miles, kilograms to pounds, Celsius to Fahrenheit — unit conversion is the small task that interrupts everything from cooking to engineering. This free metric calculator handles six quantities — length, mass, volume, temperature, area and speed — across metric and imperial units, showing your value converted into every unit at once.
Pick the quantity, enter a value, choose from/to units (or hit the swap button), and get the answer with the conversion path shown. No signup, everything runs privately in your browser.
Length · Mass · Volume · Temp · Area · Speed
Please enter a number to convert.
Result
Exact conversion factors (no rounding in the math — only in the display). Temperature uses the standard offset formulas, not a simple multiplier.
How to Use the Metric Calculator
- Select the quantity — length, mass, volume, temperature, area or speed. The unit dropdowns update automatically.
- Enter your value and pick the from and to units. The swap button (⇆) flips them instantly.
- Read the result plus a full table of every other unit — handy when a recipe, spec sheet or textbook uses something unexpected.
How Conversions Work
Temperature: °F = °C × 9/5 + 32 · K = °C + 273.15
Worked examples: 5 km → miles: 5 ÷ 1.609344 = 3.1069 mi. 100°F → °C: (100 − 32) × 5/9 = 37.78°C. 2.5 kg → lb: 2.5 ÷ 0.45359237 = 5.5116 lb.
Essential Conversion Factors
| Conversion | Factor |
|---|---|
| 1 inch | 2.54 cm (exact) |
| 1 mile | 1.609344 km (exact) |
| 1 pound | 0.45359237 kg (exact) |
| 1 gallon (US) | 3.78541 liters |
| 1 acre | 4,046.86 m² |
| 60 mph | 96.56 km/h |
Who Converts Units Daily
- Students — physics and chemistry homework is half unit conversion.
- Cooks & bakers translating US cups to metric grams and milliliters.
- Travelers reading speed limits, weather and fuel economy abroad.
- Tradespeople working from plans drawn in the “other” system.
Landmarks Worth Memorizing
A few fixed points make every other conversion easier to sanity-check. Water freezes at 0°C (32°F) and boils at 100°C (212°F). Normal body temperature is 37°C — exactly 98.6°F. A meter is a little longer than a yard (1 m = 1.094 yd), a kilogram is about 2.2 pounds, and a liter is slightly more than a US quart (1 L = 1.057 qt). And the scales meet at one famous point: −40° is the same temperature in Celsius and Fahrenheit, because −40 × 9/5 + 32 = −40.
Mental Math Shortcuts for Travelers
When the calculator is not handy, these approximations are close enough for weather, road signs and luggage scales. Kilometers to miles: multiply by 0.6 (the true factor is 0.621, so you land about 3.5% low — a 100 km drive is “about 60 miles”, really 62.1). Kilograms to pounds: multiply by 2.2. Celsius to Fahrenheit: double it and add 30 — rough, but it tells you 20°C is about 70°F (true value 68°F) before you choose a jacket. Use the calculator above whenever the number actually matters.
Frequently Asked Questions
What is the metric system?
The metric system (SI) is the decimal-based measurement system used worldwide: meters for length, kilograms for mass, liters for volume. Every unit scales by powers of ten, which makes conversion simple arithmetic.
How do you convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32: °F = °C × 9/5 + 32. So 25°C = 77°F. To go back: °C = (°F − 32) × 5/9.
How many cm are in an inch?
Exactly 2.54 cm — this one is defined, not measured, so it never varies.
What is the difference between mass and weight?
Mass (kg, lb) is how much matter something contains; weight is the gravitational force on it. On Earth the distinction rarely matters for everyday conversions, which is why the calculator groups them.
Why does the US still use imperial units?
History and inertia: retooling an entire economy’s signage, machinery and education is enormously expensive. Science, medicine and the military in the US largely use metric already.
Are UK gallons the same as US gallons?
No — a UK (imperial) gallon is 4.546 liters vs 3.785 for the US gallon, about 20% larger. This calculator uses US gallons; always check which gallon a British source means.
At what temperature are Celsius and Fahrenheit the same?
−40 degrees. It is the only point where the two scales meet: convert −40°C with the formula and you get −40 × 9/5 + 32 = −72 + 32 = −40°F. Every other temperature reads differently on the two scales.
How do I convert centimeters to feet and inches?
Divide centimeters by 2.54 to get total inches, then split into feet (12 inches each) and the remainder. Example: 175 cm ÷ 2.54 = 68.9 inches, which is 5 feet plus 8.9 inches — about 5′9″. The calculator above does this automatically for any value.
Is a liter the same as a quart?
Close, but not equal. One liter is 1.057 US quarts, so a liter is about 5.7% larger. Two liters is roughly 2.1 quarts. The difference is small enough to ignore in the kitchen and large enough to matter in a fuel tank or a chemistry lab.
Final Thoughts
Unit conversion errors have crashed spacecraft and ruined recipes — the math is trivial, but only if you actually do it. Bookmark this page and never guess between systems again.
Try our yards to tons converter.