Unit Converter: Free Online Length, Weight & Temperature Converter
Convert between common units instantly.
About the Unit Converter
Pick a category, type a value into the "From" field, and choose the units on each side — the result updates as you type, with no button to press. Converting between measurement systems is a daily need for cooks scaling a recipe, travelers checking a speed limit sign, engineers translating a spec sheet, and students working through homework. This converter covers the five most common categories — length, weight, temperature, speed, and volume — with the swap button letting you flip the direction of any conversion in one click.
How conversions work
Step 1 → Convert input to the base unit (e.g., meters for length)
Step 2 → Convert base unit to the target unit
Example → 5 miles × 1609.344 = 8046.72 m ÷ 1000 = 8.047 km
Every unit in a category routes through one shared base unit — meters for length, kilograms for weight, liters for volume, meters per second for speed, and Celsius for temperature. Converting directly from one unit to another would need a separate formula for every possible pair, which gets unwieldy fast. Routing everything through a single base means adding a new unit only requires two formulas: one in, one out.
The five categories
Length covers kilometers down to millimeters on the metric side, and miles down to inches on the imperial side. Weight spans kilograms, grams, and milligrams alongside pounds, ounces, and stone. Temperature handles the three scales you'll actually run into: Celsius, Fahrenheit, and Kelvin. Speed converts between km/h, m/s, mph, and knots, which covers everything from road signs to nautical charts. Volume handles liters and milliliters next to US gallons, quarts, pints, cups, and fluid ounces for kitchen measurements.
Common conversions to know
- 📏1 mile = 1.609 km · 1 inch = 2.54 cm · 1 foot = 30.48 cm
- ⚖️1 pound = 453.6 g · 1 stone = 6.35 kg · 1 ounce = 28.35 g
- 🌡️°F to °C: subtract 32, multiply by 5/9 · 0°C = 32°F · 100°C = 212°F
- 🧪1 US gallon = 3.785 L · 1 cup = 240 mL · 1 fl oz = 29.57 mL
Keeping a handful of these anchor conversions in your head is faster than reaching for a calculator for quick estimates. Knowing that a mile is roughly 1.6 km, for instance, lets you convert a rough running distance or a speed limit in your head well enough for everyday purposes, and you can still reach for the exact figure here when precision matters.
A note on temperature
Temperature works differently than the other categories because its scales don't share a common zero point. Converting length or weight is a straight multiplication, but Fahrenheit to Celsius needs both a multiplication and an offset — subtract 32 first, then multiply by 5/9. Kelvin sidesteps the offset problem entirely by starting at absolute zero, which is why scientific contexts favor it even though it feels unfamiliar for everyday use.
Tips for accurate results
Results are shown to six significant figures with trailing zeros stripped, which is precise enough for cooking, travel, and most schoolwork. For engineering or scientific work where rounding error compounds across multiple steps, carry extra decimal places through your own calculation rather than rounding at each intermediate conversion. And double-check which "gallon" or "ounce" you need — US and imperial versions of these units differ, and this converter uses US definitions throughout.
Common uses
Cooks use it to scale a recipe written in cups and ounces into grams and milliliters, which tends to bake more consistently than volume measurements anyway. Travelers use it to translate a road sign's speed limit or a weather forecast's temperature into units they actually understand at a glance. Students use it to check homework answers or convert between units mid-problem without breaking their flow to look up a conversion factor. Fitness trackers, recipe apps, and shopping comparisons across countries all lean on the same handful of conversions this tool covers.
Metric versus imperial, briefly
The metric system's advantage is that every unit within a category scales by powers of ten — a kilometer is always 1,000 meters, a kilogram always 1,000 grams — so converting within it is just moving a decimal point. Imperial units evolved from older, more practical origins (a foot roughly the length of a foot, a yard roughly a stride) and scale by inconsistent factors instead, which is exactly why a converter earns its keep here: nobody memorizes that a mile equals 5,280 feet, or that a gallon holds 128 fluid ounces, without a reason to use those numbers regularly.
Related: Percentage Calculator for ratio and proportion calculations.
Frequently Asked Questions
Is the Unit Converter free?
Yes — completely free. No account and no data sent to a server.
Do I need an account?
No account, no login, and no signup required.
What unit categories are supported?
Length (metric and imperial), weight/mass, temperature (Celsius, Fahrenheit, Kelvin), speed, and volume. Results update instantly as you type.
How do I convert Fahrenheit to Celsius?
Subtract 32 from the Fahrenheit value, then multiply by 5/9. Quick reference: 32°F = 0°C (freezing), 98.6°F = 37°C (body temperature), 212°F = 100°C (boiling). The calculator handles this automatically.