What Is a Conversion Calculator?
A conversion calculator translates a value from one unit of measurement to another — feet to meters, pounds to kilograms, Celsius to Fahrenheit, and so on. This one covers eight categories: length, weight, temperature, area, volume, speed, time, and digital storage. Enter a value in either field and the result appears instantly; the panel below shows your value converted into every unit in that category at once.
Two measurement systems dominate globally. The metric system (SI), used by every country except the United States, Myanmar, and Liberia, is built on base-10 arithmetic — converting kilometers to meters is just multiplying by 1,000. The US Customary system uses different factors for nearly every step: 12 inches in a foot, 3 feet in a yard, 1,760 yards in a mile. This calculator handles both, including the less obvious conversions like US gallons vs UK Imperial gallons (which differ by 20%). Reference: NIST — SI Unit Conversions
How to Use This Converter
- Pick a category — Length, Weight, Temperature, Area, Volume, Speed, Time, or Data
- Enter your value in the left field (From) — results update as you type, no button needed
- Select units from both dropdowns — swap them anytime with the ⇄ button
- See all conversions in the panel below — your value converted to every unit in that category at once
- Type in the right field too — entering a result converts backward to the From unit
Temperature — The Only Conversion With Two Steps
Every other unit conversion in this calculator is a single multiplication or division. Temperature is the exception — the Celsius and Fahrenheit scales have different zero points, so conversion requires both multiplication and an offset. Here are the formulas exactly as this calculator applies them:
Length Conversions
The international inch is defined as exactly 2.54 cm, which anchors every other US-to-metric length conversion. All the values below flow from that single definition:
| From | To Metric | Reverse | Common Use |
|---|---|---|---|
| 1 inch | 2.54 cm exactly | 1 cm = 0.3937 in | Screen sizes, clothing |
| 1 foot | 0.3048 m exactly | 1 m = 3.28084 ft | Heights, room dimensions |
| 1 yard | 0.9144 m exactly | 1 m = 1.09361 yd | Football fields, fabric |
| 1 mile | 1.60934 km | 1 km = 0.621371 mi | Road distances, running |
| 1 nautical mile | 1.852 km exactly | 1 km = 0.5400 nmi | Aviation, maritime |
| 1 light-year | 9.461 × 10¹⁵ m | — | Astronomy |
The "exactly" notation means these are defined values, not measured approximations. The international inch has been 2.54 cm by definition since 1959, per agreement between the US, UK, and Commonwealth nations. Source: NIST — SI Units of Length
Weight and Mass Conversions
Technically, "weight" is a force (measured in newtons) and "mass" is the quantity of matter (kilograms) — but in everyday use, the terms are interchangeable. All values below are mass conversions at standard Earth gravity:
| From | To Metric | Reverse | Common Use |
|---|---|---|---|
| 1 ounce (oz) | 28.3495 g | 1 g = 0.035274 oz | Food portions, mail |
| 1 pound (lb) | 0.453592 kg | 1 kg = 2.20462 lb | Body weight, groceries |
| 1 stone | 6.35029 kg | 1 kg = 0.157473 stone | Body weight in UK |
| 1 short ton (US) | 907.185 kg | 1 tonne = 1.10231 short tons | Freight, cargo (US) |
| 1 long ton (UK) | 1,016.05 kg | — | Freight (UK) |
| 1 metric tonne | 1,000 kg exactly | — | International trade |
Volume Conversions
Volume has a hidden complication: US and UK gallons are different units with the same name. A US gallon is 3.785 liters; a UK (Imperial) gallon is 4.546 liters — a 20% difference. Fuel economy specs in miles per gallon mean different things on each side of the Atlantic because of this gap:
| From | To Liters | Notes |
|---|---|---|
| 1 US gallon | 3.78541 L | Used in US fuel, milk, etc. |
| 1 UK (Imperial) gallon | 4.54609 L | Used in UK/Australia fuel economy |
| 1 US quart | 0.946353 L | 4 US quarts = 1 US gallon |
| 1 US pint | 0.473176 L | UK pint = 0.568261 L (different!) |
| 1 US cup | 0.236588 L (236.6 ml) | Standard US recipe measurement |
| 1 US fluid ounce | 29.5735 ml | UK fl oz = 28.413 ml |
| 1 liter | 33.814 US fl oz | Standard metric bottle size |
Kitchen Measurement Reference
Recipe measurements use a chain: teaspoons → tablespoons → cups → pints → quarts → gallons. Every row below flows from the same definition — 1 US tablespoon = 3 teaspoons = 14.787 ml:
| Measure | Teaspoons | Tablespoons | ml | fl oz |
|---|---|---|---|---|
| 1 teaspoon | 1 | ⅓ | 4.93 | 0.167 |
| 1 tablespoon | 3 | 1 | 14.79 | 0.5 |
| ¼ cup | 12 | 4 | 59.15 | 2 |
| ⅓ cup | 16 | 5⅓ | 78.86 | 2.67 |
| ½ cup | 24 | 8 | 118.29 | 4 |
| 1 cup | 48 | 16 | 236.59 | 8 |
| 1 pint | 96 | 32 | 473.18 | 16 |
| 1 quart | 192 | 64 | 946.35 | 32 |
5 Practical Tips for Unit Conversion
- Know your gallon — US or UK. A recipe calling for "1 gallon" means something different in London than in Los Angeles. US gallon = 3.785 L; UK gallon = 4.546 L. For fuel economy, 30 MPG (US) ≈ 36 MPG (UK) because the UK gallon is 20% larger. When buying car specs internationally, verify which standard is being used.
- For rough °C ↔ °F estimates, use the "double and add 30" rule. It's not exact but gets you within 5°F for everyday temperatures: 25°C → double 25 = 50, add 30 = 80°F (actual: 77°F). Good enough to know whether to pack a coat. For body temperature, cooking, and precision work, use the exact formula.
- US short ton vs metric tonne: a 10% difference that matters in freight. 1 short ton (US) = 2,000 lbs = 907.2 kg. 1 metric tonne = 2,204.6 lbs = 1,000 kg. A commodity contract in metric tonnes vs short tons changes the quantity by about 10%. Always check which unit a contract, shipping manifest, or bulk order is using.
- Speed conversions between mph and km/h have a useful shorthand. 1 mph ≈ 1.609 km/h, so 60 mph = 96.56 km/h. A rough mental conversion: multiply mph by 1.6. Driving in a metric country at 100 km/h is 62.1 mph — just below a US highway's 65 mph limit. The reverse: divide km/h by 1.6 to get approximate mph.
- Digital storage: 1,024 not 1,000. Storage uses binary prefixes (1 KB = 1,024 bytes, not 1,000), which is why a "500 GB" hard drive shows up as ~465 GB in Windows — the OS reports in base-1,024 but the drive is labeled in base-1,000. A 500 × 10⁹ byte drive ÷ 1,073,741,824 = 465.7 binary GB. This is not a defect; it's two different conventions using the same unit names.