Lifestyle · Conversion
Unit Converter
Convert between imperial and metric units instantly — length, weight and temperature. Miles to km, lbs to kg, Fahrenheit to Celsius and more. Free and no sign-up.
How the unit converter works
This tool converts between US customary (imperial) units and the metric system used by most of the world. Pick a category, type a value, and choose the conversion direction. The result updates in real time and shows the exact formula used.
- Length — miles to km (× 1.60934), feet to meters (× 0.3048), inches to centimeters (× 2.54), and each in reverse.
- Weight — pounds to kilograms (× 0.453592), ounces to grams (× 28.3495), and each in reverse.
- Temperature — Fahrenheit to Celsius using C = (F − 32) × 5/9, and Celsius to Fahrenheit using F = C × 9/5 + 32.
Common conversion factors
| From → To | Factor / formula |
|---|---|
| Miles → Kilometers | × 1.60934 |
| Feet → Meters | × 0.3048 |
| Inches → Centimeters | × 2.54 |
| Pounds → Kilograms | × 0.453592 |
| Ounces → Grams | × 28.3495 |
| Fahrenheit → Celsius | (F − 32) × 5/9 |
Things to keep in mind
Rounding
Conversion factors like 1.60934 are themselves rounded approximations of exact values. For everyday use the result shown here is accurate, but for engineering, scientific or legal work you should use full-precision factors and an official reference.
Imperial vs US customary
This converter uses US customary units, which match imperial units for length and temperature. Some volume and weight units differ between the UK imperial system and the US system, so double-check before converting recipes or fuel economy figures across regions.
Frequently asked questions
How do I convert miles to kilometers?
Multiply miles by 1.60934. For example, 10 miles × 1.60934 = 16.0934 km. To reverse it, divide kilometers by 1.60934.
How do I convert pounds to kilograms?
Multiply pounds by 0.453592. For example, 150 lbs = 68.04 kg. To go back, divide kilograms by 0.453592.
What is the Fahrenheit to Celsius formula?
Subtract 32, then multiply by 5/9: C = (F − 32) × 5/9. To go the other way: F = C × 9/5 + 32.
Why does most of the world use metric?
The metric system is decimal-based, so units scale by tens, making math simpler. Only the US, Liberia and Myanmar still rely mainly on imperial units day to day.
Is this converter accurate?
Yes — it uses internationally defined factors and rounds sensibly. For engineering or legal precision, verify against an official reference.
Metric vs. imperial: a short history
Almost every conversion headache comes down to one fact: the world uses two different measurement systems. Understanding where they came from makes it easier to remember which is which — and why you so often need a converter in the first place.
How the metric system began
The metric system was created in France in the 1790s, during the French Revolution, as a deliberate attempt to replace a tangle of local units with one rational, decimal-based standard. Its defining feature is that everything scales by powers of ten: 1,000 meters in a kilometer, 100 centimeters in a meter, 1,000 grams in a kilogram. That decimal structure is why metric math is usually just moving a decimal point. Over the following two centuries the system was refined into the International System of Units (the SI), which is now the official measurement standard of science and of nearly every country on Earth.
Where the imperial system came from
Imperial units grew up the opposite way — organically, over centuries, from human-scale references. A foot was roughly the length of a foot; an inch was about the width of a thumb; a pound traces back to old trade weights. The British Empire standardized these into the imperial system in 1824, and the United States developed a closely related set known as US customary units. Because they evolved rather than being designed, the relationships are irregular: 12 inches in a foot, 3 feet in a yard, 1,760 yards in a mile. There is no decimal logic to memorize — just historical conventions.
Why the United States still uses imperial
The US is the most prominent country that still relies on customary units for everyday life, alongside Liberia and Myanmar. This is mostly inertia: by the time the metric system gained global momentum, American industry, road signs, tools, and habits were already built around feet, pounds, and Fahrenheit. Switching everything over would be enormously expensive and disruptive, so the country mostly kept its familiar units for daily use while science, medicine, and the military adopted metric. The result is the everyday split most travelers notice — and the reason a converter is so handy.
The conversions you'll actually use
Most day-to-day conversions fall into four buckets: length, weight, temperature, and volume. Here are the formulas worth knowing, with the exact factors this tool uses.
Length
- Miles ↔ kilometers: km = miles × 1.60934; miles = km ÷ 1.60934. A quick mental shortcut: a kilometer is about 0.62 miles, so a 5K run is roughly 3.1 miles.
- Feet ↔ meters: m = feet × 0.3048; feet = m ÷ 0.3048. One meter is a little over 3 feet 3 inches.
- Inches ↔ centimeters: cm = inches × 2.54; inches = cm ÷ 2.54. This factor is exact by international agreement.
Weight
- Pounds ↔ kilograms: kg = lbs × 0.453592; lbs = kg ÷ 0.453592. A handy estimate is that 1 kg is about 2.2 lbs.
- Ounces ↔ grams: g = oz × 28.3495; oz = g ÷ 28.3495.
Temperature
Temperature is the one conversion that is not a simple multiplication, because the two scales have different zero points. To go from Fahrenheit to Celsius: C = (F − 32) × 5/9. To go the other way: F = C × 9/5 + 32. A useful anchor is that the scales meet at −40°, where −40°F equals −40°C.
Volume (good to know)
This converter focuses on length, weight, and temperature, but volume is the trickiest area because the US and UK define some units differently. A US gallon is about 3.785 liters, while a UK (imperial) gallon is about 4.546 liters. That gap is exactly why you should never copy fuel-economy or recipe figures between regions without checking which gallon is meant.
Quick reference: common values
| Everyday value | Converts to |
|---|---|
| 1 mile | 1.609 km |
| 5 km | 3.107 mi |
| 6 ft | 1.829 m |
| 150 lbs | 68.04 kg |
| 1 kg | 2.205 lbs |
| 12 oz | 340.2 g |
Temperature at a glance
| Fahrenheit | Celsius |
|---|---|
| 32 °F (freezing) | 0 °C |
| 68 °F (room temp) | 20 °C |
| 98.6 °F (body temp) | 37 °C |
| 212 °F (boiling) | 100 °C |
Common conversion mistakes to avoid
- Adding before multiplying with temperature. The most frequent error is forgetting the order of operations. For Fahrenheit to Celsius you must subtract 32 first, then multiply by 5/9 — not the other way around.
- Mixing up US and UK volume units. A US gallon and a UK gallon are not the same, and neither are US and UK fluid ounces. Always confirm which system a recipe or fuel figure uses.
- Confusing weight and mass in casual speech. In everyday use, pounds and kilograms are treated as interchangeable for "how heavy is it," and that is fine here — just know that in physics they are technically different concepts.
- Over-rounding early. If you round 1.60934 down to 1.6 at the start of a long calculation, small errors pile up. Keep full precision until the final step, then round.
- Reversing the factor. Multiplying when you should divide is easy to do. A quick sanity check: kilometers should be a bigger number than the miles you started with, and pounds should be bigger than the kilograms.
When everyday conversions show up
You will reach for these more often than you think. Travelers convert road-sign distances and weather forecasts; home cooks adapt recipes written in grams and milliliters; fitness apps report weight in kilograms while a US scale shows pounds; and anyone shopping online from another country has to translate clothing and shipping dimensions. Keeping the core factors — 1.60934 for miles, 0.453592 for pounds, 2.54 for inches, and the Fahrenheit/Celsius formula — close at hand covers the vast majority of real-life situations.
More conversion questions
How do I convert feet to meters?
Multiply the number of feet by 0.3048. For example, 6 ft × 0.3048 = 1.829 m. To convert meters back to feet, divide by 0.3048.
How do I convert inches to centimeters?
Multiply inches by 2.54, a factor that is exact by international definition. For example, 10 in × 2.54 = 25.4 cm. To reverse it, divide centimeters by 2.54.
How do I convert kilograms to pounds quickly in my head?
Multiply by roughly 2.2. So 70 kg is about 154 lbs. For an exact answer, divide kilograms by 0.453592.
What is 100°F in Celsius?
Using C = (F − 32) × 5/9: (100 − 32) × 5/9 = 37.78 °C. That is close to human body temperature, which is about 98.6 °F or 37 °C.
Is a US gallon the same as a UK gallon?
No. A US gallon is about 3.785 liters, while a UK (imperial) gallon is about 4.546 liters — roughly 20% larger. Always check which gallon a figure refers to before converting.
Why is the inch-to-centimeter factor exactly 2.54?
Since 1959, the inch has been defined internationally as exactly 2.54 centimeters. Unlike many conversion factors, this one is not a rounded approximation — it is exact by agreement.