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Unit Conversions

Free unit converters: length, weight, temperature, volume, speed, area, data storage, cooking measurements, pressure, energy and Roman numerals — exact factors.

11 calculators Free and online

📌 About Unit Conversions

Switching between US and metric units shouldn't slow you down. These converters handle the everyday swaps — feet to centimeters, pounds to kilograms, Fahrenheit to Celsius — and the less common ones too: volume, speed, area, data storage, pressure, energy, cooking measurements and even Roman numerals. Each uses the exact conversion factor so you can trust the number.

Every tool converts in both directions and lists the value in several common units at once, so whether you're reading a recipe, a spec sheet, a hard drive label or a weather report from abroad, the answer is right there with a full reference table.

  • Length, weight and temperature: feet/cm, pounds/kg, Fahrenheit/Celsius
  • Volume and cooking: gallons, liters, cups, tablespoons and cup-to-grams
  • Speed (mph ↔ km/h), area (acres, hectares), pressure (psi ↔ bar) and energy (cal ↔ joules)
  • Data storage (MB ↔ GB, decimal vs binary) and Roman numerals (both directions)
  • See the exact conversion factor and common equivalents every time

🧮 Calculators in this category

Numbers

Roman Numeral Converter — Number to Roman & Roman to Number
Convert any whole number from 1 to 3999 into Roman numerals, or decode a Roman numeral back into a number — using exact standard subtractive notation.
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Speed

Speed Converter — mph, km/h, m/s, ft/s & Knots
Convert any speed between miles per hour, kilometers per hour, meters per second, feet per second and knots — with exact factors and a full reference table.
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Area

Area Converter — Square Feet, Acres, Hectares & Metric
Convert any area between square feet, square inches, square yards, acres, square miles, square centimeters, square meters, hectares and square kilometers — with an exact table.
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Cooking

Cooking Measurement Converter — Teaspoons, Tablespoons, Cups & mL
Convert recipe amounts between teaspoons, tablespoons, cups, fluid ounces, mL and liters — plus cup-to-grams for flour, sugar and butter, with exact US factors.
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Data

Data Storage Converter — Bits, Bytes, KB, MB, GB & TB
Convert digital storage between bits, bytes, KB, MB, GB, TB and the binary KiB/MiB/GiB units — with the exact 1000-vs-1024 factors and a full table.
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Energy

Energy Converter — Calories, Joules, kWh, BTU & More
Convert energy between joules, kilojoules, calories, food Calories (kcal), watt-hours, kWh, BTU, foot-pounds and electronvolts — with an exact table.
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Pressure

Pressure Converter — PSI, Bar, kPa, atm, mmHg & More
Convert pressure between psi, bar, kPa, atmospheres, mmHg (torr), inHg and kg/cm² — with exact factors and a full conversion table.
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Volume

Volume Converter — Gallons, Liters, Cups, Quarts & Cubic Feet
Convert any volume between US and imperial gallons, liters, milliliters, quarts, pints, cubic feet, cubic inches and cubic meters — with an exact conversion table.
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Length & Distance

Length Converter — Inches, Feet, Yards, Miles & Metric
Convert any length between inches, feet, yards, miles, millimeters, centimeters, meters and kilometers — with an exact conversion table.
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Temperature

Temperature Converter — Fahrenheit to Celsius, Kelvin & Back
Convert between Fahrenheit, Celsius and Kelvin in one click — and see all three scales side by side with the formula shown.
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Weight & Mass

Weight Converter — Ounces, Pounds, Tons, Grams & Kilograms
Convert weight fast between ounces, pounds, US tons, milligrams, grams, kilograms and metric tonnes — with the exact factors and an equivalents table.
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📝 Related articles

Read more about this topic on our blog.

Cups to mL: A Complete Kitchen Conversion Guide
One US cup equals 236.6 mL, but cup-to-grams depends entirely on the ingredient. Here's the math behind cups, tablespoons, and teaspoons, plus a handy conversion table.
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mph to km/h: Everyday Speed Conversions Made Easy
1 mph equals exactly 1.609344 km/h. Here are the quick mental tricks, the m/s and knots conversions, foreign speed limits, and a table for 30, 55, 65, and 70 mph.
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Roman Numerals Explained: How to Read and Write Them
Roman numerals use just seven letters to build any number from 1 to 3,999. Here's how additive and subtractive notation work, with worked examples like 2024 = MMXXIV.
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❓ Frequently asked questions

How do I convert Fahrenheit to Celsius?

Subtract 32, then multiply by 5/9. For example, 98.6°F − 32 = 66.6, × 5/9 = 37°C. To go the other way: multiply by 9/5 and add 32.

How many centimeters are in a foot?

One foot equals exactly 30.48 centimeters, since one inch is 2.54 cm and there are 12 inches in a foot.

Why is 1 GB sometimes 1000 MB and sometimes 1024 MB?

Storage marketed in GB uses decimal units (1 GB = 1000 MB = 1,000,000,000 bytes), while operating systems often count in binary (1 GiB = 1024 MiB). The data storage converter shows both so the mismatch makes sense.

Is a US gallon the same as an imperial gallon?

No. A US gallon is about 3.785 liters and an imperial (UK) gallon is about 4.546 liters — roughly 20% larger. The volume converter lets you pick the right one.