Unit Converter (Length, Mass, Volume, Temperature & More)
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A unit converter multiplies your value by an exact conversion factor. One mile is exactly 1.609344 kilometers, so 5 miles × 1.609344 = 8.04672 km. Temperature works differently because the scales start at different zeros: °C = (°F − 32) × 5/9, so 72 °F is about 22.22 °C. The tool below covers 13 kinds of measurement and shows every step.
Exact NIST and SI factors
Show steps
- Both units have exact definitions in meters (m): 1 mi = 1,609.344 m and 1 km = 1,000 m.
- Chain the factors (dimensional analysis): 5 mi × (1,609.344 m / 1 mi) × (1 km / 1,000 m). The mi and m cancel, leaving kilometers.
- 1 mile = 1.609344 km, so multiply by 1.609344.
- Multiply: 5 × 1.609344 = 8.04672 km.
- Check by converting back: 8.04672 km ÷ 1.609344 = 5 mi.
| Unit | Value | Exact definition |
|---|---|---|
| 1 nm = 10⁻⁹ m | 8,046,720,000,000 nm | 1 nm = 10⁻⁹ m |
| 1 µm = 10⁻⁶ m | 8,046,720,000 µm | 1 µm = 10⁻⁶ m |
| 1 mm = 0.001 m | 8,046,720 mm | 1 mm = 0.001 m |
| 1 cm = 0.01 m | 804,672 cm | 1 cm = 0.01 m |
| m (SI unit) | 8,046.72 m | m (SI unit) |
| 1 km = 1,000 m | 8.04672 km | 1 km = 1,000 m |
| 1 in = 0.0254 m | 316,800 in | 1 in = 0.0254 m |
| 1 ft = 0.3048 m | 26,400 ft | 1 ft = 0.3048 m |
| 1 yd = 0.9144 m | 8,800 yd | 1 yd = 0.9144 m |
| 1 mi = 1,609.344 m | 5 mi | 1 mi = 1,609.344 m |
| 1 nmi = 1,852 m | ≈ 4.34488 nmi | 1 nmi = 1,852 m |
| 1 au = 1.495978707 × 10¹¹ m | ≈ 5.3789 × 10⁻⁸ au | 1 au = 1.495978707 × 10¹¹ m |
Tap a unit name to make it the “To” unit. Highlighted: your answer.
| Miles (mi) | Kilometers (km) |
|---|---|
| 1 | ≈ 1.60934 |
| 2 | ≈ 3.21869 |
| 3 | ≈ 4.82803 |
| 4 | ≈ 6.43738 |
| 5 | 8.04672 |
| 10 | ≈ 16.0934 |
| 15 | ≈ 24.1402 |
| 20 | ≈ 32.1869 |
| 25 | 40.2336 |
| 50 | 80.4672 |
| 100 | ≈ 160.934 |
| 250 | 402.336 |
| 500 | 804.672 |
| 1,000 | ≈ 1,609.34 |
Your value is highlighted. ≈ marks a rounded value.
How to use the unit converter
- Pick the kind of measurement: length, mass, temperature, volume, area, speed, time, data, energy, power, pressure, force or angle.
- Type a number in the From box and choose its unit. Decimals, fractions (3 1/2), scientific notation (1.5e-9) and, for angles, multiples of π (π/4) all work.
- Choose the unit you want in the To box. The answer updates as you type, and you can type in the To box to convert the other way.
- Or type the whole question in the shortcut box, such as 72 F to C or 3 cups in mL.
- Open Show steps for the working, then read the table below it to see the same value in every unit of that kind.
Each answer is tagged exact or rounded. The converter stores every factor as an exact fraction, so 5 miles really is 8.04672 km, not 8.0467199.
How unit conversion works
A conversion factor is a fraction equal to 1, such as 1,609.344 m / 1 mi. Multiplying by it changes the units without changing the amount. When neither unit is the base unit, chain two factors through it (this is called dimensional analysis or the factor-label method):
5 mi × (1,609.344 m / 1 mi) × (1 km / 1,000 m) = 8,046.72 km ÷ 1,000 = 8.04672 km
The miles cancel in the first fraction and the meters cancel in the second, so only kilometers are left. If the units do not cancel, the factor is upside down.
Every unit in this converter is defined exactly in terms of an SI unit. Since 1959 the inch has been exactly 2.54 cm and the pound exactly 0.45359237 kg, so customary units convert to metric with no rounding at all.
Unit conversion examples
Temperature: 72 °F to °C
Subtract 32 first, then multiply by 5/9: (72 − 32) × 5/9 = 40 × 5/9 = 200/9 ≈ 22.22 °C. To go from Celsius to Kelvin, add 273.15. A temperature change only uses the scale factor: a rise of 10 °C is a rise of 18 °F.
Area: 150 square feet to square meters
One foot is 0.3048 m, so one square foot is 0.3048 × 0.3048 = 0.09290304 m². Then 150 ft² × 0.09290304 = 13.935456 m². Using 0.3048 instead of its square is the most common area mistake; for volume, cube the length factor.
Speed: 60 mph to meters per second
Chain the length and time factors: 60 mi/h × 1,609.344 m/mi ÷ 3,600 s/h = 26.8224 m/s, exactly. The same chain gives 60 mph ≈ 96.5606 km/h.
Data: 5 GB to GiB
A gigabyte (GB) is 1,000,000,000 bytes, while a gibibyte (GiB) is 230 = 1,073,741,824 bytes. So 5 GB = 5,000,000,000 ÷ 1,073,741,824 ≈ 4.66 GiB, which is why a new drive looks smaller in some operating systems.
Exact conversion factors
| Quantity | Unit | Exact value |
|---|---|---|
| Length | 1 inch | 2.54 cm |
| Length | 1 foot | 0.3048 m |
| Length | 1 mile | 1,609.344 m |
| Length | 1 nautical mile | 1,852 m |
| Mass | 1 pound | 0.45359237 kg |
| Mass | 1 ounce | 28.349523125 g |
| Volume | 1 US gallon | 231 in³ = 3.785411784 L |
| Volume | 1 imperial gallon | 4.54609 L |
| Volume | 1 US fluid ounce | 29.5735295625 mL |
| Area | 1 acre | 43,560 ft² = 4,046.8564224 m² |
| Area | 1 hectare | 10,000 m² |
| Speed | 1 mile per hour | 0.44704 m/s |
| Speed | 1 knot | 1,852 m per hour |
| Temperature | °C to K | K = °C + 273.15 |
| Temperature | °F to °C | °C = (°F − 32) × 5/9 |
| Energy | 1 calorie (thermochemical) | 4.184 J |
| Energy | 1 kilowatt-hour | 3,600,000 J |
| Energy | 1 electronvolt | 1.602176634 × 10−19 J |
| Pressure | 1 standard atmosphere | 101,325 Pa |
| Pressure | 1 bar | 100,000 Pa |
| Force | 1 pound-force | 4.4482216152605 N |
| Power | 1 horsepower (mechanical) | 550 ft·lbf/s ≈ 745.7 W |
| Data | 1 kibibyte (KiB) | 1,024 bytes |
| Angle | 1 degree | π/180 rad |
Metric prefixes
Metric units change by powers of ten, so converting inside the metric system only moves the decimal point.
| Prefix | Symbol | Factor | Example |
|---|---|---|---|
| nano | n | 10−9 | 1 nm = 0.000000001 m |
| micro | µ | 10−6 | 1 µs = 0.000001 s |
| milli | m | 10−3 | 1 mL = 0.001 L |
| centi | c | 10−2 | 1 cm = 0.01 m |
| kilo | k | 103 | 1 kg = 1,000 g |
| mega | M | 106 | 1 MW = 1,000,000 W |
| giga | G | 109 | 1 GB = 1,000,000,000 bytes |
Binary prefixes for computer memory use powers of 2 instead: kibi (Ki) = 1,024, mebi (Mi) = 1,024², gibi (Gi) = 1,024³.
Unit conversion on tests and homework
Unit conversion appears on the SAT, ACT and state tests, usually inside a rate problem. A typical question: a car travels at 45 miles per hour; how many feet per second is that? Write the factors so the units cancel: 45 mi/h × 5,280 ft/mi ÷ 3,600 s/h = 66 ft/s. Tests often give the factor (5,280 feet in a mile), so the skill is setting up the fractions, not memorizing numbers.
Before you type a problem in, decide which unit you have and which you need, and estimate. A kilometer is a bit more than half a mile, so 5 miles should be about 8 km. If the converter’s answer is far from your estimate, check the units you picked. Work small problems by hand to practice the factor-label method, and use the converter to check your answer and to handle long factors such as 0.45359237.
Common unit conversion mistakes
- Flipping the factor. Converting to a smaller unit gives a bigger number. 3 m is 300 cm, not 0.03 cm.
- Not squaring or cubing. 1 m = 100 cm, but 1 m² = 10,000 cm² and 1 m³ = 1,000,000 cm³.
- Treating temperature like length. 20 °C is not 40 °F; it is 20 × 9/5 + 32 = 68 °F.
- Mixing US and imperial volumes. A US gallon is about 3.785 L; an imperial gallon is 4.546 L.
- Confusing GB and GiB, or bits and bytes: a 100 Mbit/s connection moves 12.5 MB per second.
- Rounding too early. Keep the full factor until the last step, then round once.
Sources
All factors were checked November 2026 against these primary sources:
- NIST Special Publication 811, Guide for the Use of the SI, Appendix B.9: factors by kind of quantity
- NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement
- BIPM, The International System of Units (SI Brochure), 9th edition, updated 2026
- NIST, Prefixes for binary multiples (IEC 60027-2)
Unit conversion practice quiz: 10 questions
Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.
A mile is 5,280 feet and a foot is exactly 0.3048 m, so 1 mile = 5,280 × 0.3048 = 1,609.344 m = 1.609344 km. The value 0.621371 is miles per kilometer, the other way round.
Subtract 32 first, then multiply by 5/9: (68 − 32) × 5/9 = 36 × 5/9 = 20 °C. Multiplying 68 by 5/9 without subtracting 32 gives 37.78, which is wrong.
One yard is 3 feet, and area uses the square of the length factor: 3 × 3 = 9 square feet. 27 is the number of cubic feet in a cubic yard.
One pound is exactly 0.45359237 kg, so divide: 2.5 ÷ 0.45359237 = 5.5116…, about 5.51 lb. Multiplying by 0.45359237 gives 1.13, which converts the wrong way.
Binary prefixes use powers of 1,024: 1 GiB = 1,024³ = 2³⁰ = 1,073,741,824 bytes. One gigabyte (GB) is 1,000,000,000 bytes, and 1,048,576 bytes is one mebibyte.
45 mi/h × 5,280 ft/mi ÷ 3,600 s/h = 237,600 ÷ 3,600 = 66 ft/s. Dividing by 60 instead of 3,600 gives feet per minute (3,960), not feet per second.
A liter is a cubic decimeter. One meter is 10 decimeters, so 1 m³ = 10 × 10 × 10 = 1,000 dm³ = 1,000 L.
Subtract 273.15 from the kelvin value: 300 − 273.15 = 26.85 °C. Adding 273.15 gives 573.15, which goes the wrong way.
Multiply by 180/π: π/3 × 180/π = 180/3 = 60°. The number 1.047 is π/3 itself, still in radians.
One standard atmosphere is exactly 101,325 Pa = 101.325 kPa, so 100 ÷ 101.325 = 0.9869…, about 0.99 atm. Dividing the other way, 101.325 ÷ 100, gives 1.01.
Quiz complete
Frequently asked questions
How do you convert units of measurement?
Multiply by a conversion factor written as a fraction equal to 1, with the unit you want on top and the unit you have on the bottom. For example, 12 ft × (0.3048 m / 1 ft) = 3.6576 m. For temperature, use the formula for the two scales instead.
How do you convert units of length?
Use the exact definitions 1 in = 2.54 cm, 1 ft = 12 in, 1 yd = 3 ft and 1 mi = 5,280 ft. Inside the metric system, move the decimal point: 1 km = 1,000 m = 100,000 cm.
How do you convert mm to inches?
Divide by 25.4, because one inch is exactly 25.4 mm. So 10 mm ÷ 25.4 ≈ 0.3937 in, and 100 mm ≈ 3.937 in.
How do you convert temperature units?
Use °C = (°F − 32) × 5/9, °F = °C × 9/5 + 32 and K = °C + 273.15. Water freezes at 0 °C = 32 °F = 273.15 K and boils at 100 °C = 212 °F at sea level.
How do you convert units of area?
Square the length factor. Since 1 ft = 12 in, 1 ft² = 12 × 12 = 144 in², and since 1 yd = 3 ft, 1 yd² = 9 ft². For volume, cube it: 1 yd³ = 27 ft³.
Is unit conversion on the SAT?
Yes. The SAT math section includes questions on units, rates and ratios, often inside a word problem about speed, density or cost. The factor is usually given, and you need to set up the conversion so the units cancel.
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