The Unit Conversion Calculator instantly and accurately converts values between measurement units.
Supports 5 categories: length (9 units), weight (7 units), volume (8 units), area (8 units), and speed (4 units). Converts to all units at once in a single click.
Calculator information
📋 How to use this calculator
- Choose a category: length, weight (mass), volume, area, or speed.
- Enter the numeric value to convert in the main input field.
- Pick the source unit from the dropdown (e.g., meter, kilogram, gallon, acre).
- The calculator instantly shows the conversion to ALL units in the category in real time.
- Copy the result to your clipboard with the Copy button for use in documents or spreadsheets.
- Use the Swap button to reverse the conversion direction (source <-> target).
- Tip: SI (Système International) uses meter, kilogram, and second as base units; use SI for scientific publication.
🧮 Standard SI and U.S. Customary Conversion Factors
Target Value = Source Value × Conversion Factor
- Length: 1 m = 100 cm = 3.2808 ft = 39.3701 in; 1 mile = 1,609.344 m
- Weight: 1 kg = 1,000 g = 2.2046 lb; 1 metric ton = 1,000 kg; 1 oz (avoirdupois) = 28.3495 g
- Volume: 1 L = 1,000 mL = 0.2642 US gal; 1 m³ = 1,000 L; 1 US gal = 3.7854 L
- Area: 1 hectare = 10,000 m² = 2.4711 acres; 1 km² = 100 hectares; 1 acre = 43,560 sq ft
- Speed: 1 m/s = 3.6 km/h = 2.2369 mph = 1.9438 knots
The U.S. customary system uses different fluid ounces, gallons, and tons than UK Imperial. 1 US gallon = 3.7854 L; 1 UK gallon = 4.5461 L.
💡 Worked example: Convert 5 km to various length units
Steps:- To meters: 5 × 1,000 = 5,000 m.
- To centimeters: 5,000 × 100 = 500,000 cm.
- To millimeters: 500,000 × 10 = 5,000,000 mm.
- To feet: 5,000 × 3.2808 = 16,404 ft.
- To inches: 16,404 × 12 = 196,850 in.
- To miles: 5,000 ÷ 1,609.344 = 3.1069 mi.
- To yards: 5,000 × 1.0936 = 5,468 yd.
Result: 5 km = 5,000 m = 16,404 ft = 3.11 mi = 5,468 yd.
❓ Frequently asked questions
What's the difference between U.S. customary and metric (SI) units?
U.S. customary units (inch, foot, pound, gallon) derive from British Imperial but with key differences (e.g., US gallon = 3.7854 L vs. UK gallon = 4.5461 L). The metric SI system (meter, kilogram, liter) is used in nearly every country and in all scientific publications. The U.S. is one of three countries still using customary units for daily commerce, alongside Liberia and Myanmar. Federal agencies like NIST officially endorse SI for science and federally funded research.
Why does the U.S. still use customary units?
The U.S. legally adopted the metric system through the Metric Conversion Act of 1975 (Public Law 94-168), but adoption is voluntary outside of science, the military, and federal contracts. Customary units persist in retail, road signage, and construction due to legacy infrastructure and consumer familiarity. NIST encourages SI for trade and exports. Pharmaceutical and nutritional labels use both systems under FDA rules.
How do you convert Celsius, Fahrenheit, and Kelvin?
Unlike linear conversions, temperature has an offset. °F = °C × 9/5 + 32 (e.g., 30°C = 86°F). K = °C + 273.15 (absolute temperature, can't be negative). The U.S. uses Fahrenheit for weather; Celsius is standard nearly everywhere else and in science. Kelvin is the SI standard for physics and chemistry (water triple point = 273.16 K). Absolute zero = 0 K = -273.15°C = -459.67°F.
What's the difference between a statute mile and a nautical mile?
A statute mile = 1,609.344 meters and is used for land distance in the U.S. and UK. A nautical mile = 1,852 meters, used for marine and air navigation, defined as 1/60 of a degree of latitude. Ship and aircraft speed is measured in knots = 1 nautical mile/hour = 1.852 km/h. The U.S. Coast Guard and FAA both use nautical miles, while road distances use statute miles.
What is the official measurement standard in the United States?
The National Institute of Standards and Technology (NIST) maintains U.S. measurement standards based on the SI system. For commerce, NIST Handbook 44 sets the requirements for weighing and measuring devices (scales, gas pumps), enforced by state weights-and-measures officials. Tampering with retail scales or pumps is a federal and state offense. Federally funded research and most agencies (FDA, EPA, USDA) require SI units in technical reporting.
📚 Sources & references
Last updated: May 11, 2026