How to Use the Unit Converter

The Tooldit Unit Converter handles 8 categories of measurement with metric and imperial units side by side. Conversion happens in your browser the instant you type — no submit button, no data leaving your device.

Pick a category tab at the top — Length, Weight, Temperature, Volume, Speed, Area, Time, or Data. The unit dropdowns auto-update with that category's units.
Choose the source unit from the "From" dropdown. Each option shows the short code plus the full name (e.g. "m — Meter").
Type a value into the From field. The result updates as you type.
Choose the target unit from the "To" dropdown. The selected source unit is greyed out so you can't pick the same on both sides.
Use the ⇅ swap button to flip the direction, or click any Quick conversion chip below to set both units and a common value in one tap.

Categories Supported

Length: millimeter, centimeter, meter, kilometer, inch, foot, yard, mile, nautical mile.
Weight / Mass: milligram, gram, kilogram, metric ton, ounce, pound, stone, US ton, UK ton.
Temperature: Celsius, Fahrenheit, Kelvin.
Volume: milliliter, liter, cubic meter, teaspoon, tablespoon, fluid ounce, cup, pint, quart, US gallon, UK gallon.
Speed: meters per second, km/h, mph, knot, feet per second.
Area: square millimeter, square centimeter, square meter, square kilometer, square inch, square foot, square yard, acre, hectare.
Time: millisecond, second, minute, hour, day, week, month (average), year.
Data: bit, byte, KB, MB, GB, TB (decimal) plus KiB, MiB, GiB, TiB (binary).

Why Unit Conversion Matters

Unit conversion is one of those everyday tasks that's trivial when you've got a calculator handy and treacherous when you don't. Engineers, scientists, cooks, athletes, travellers, and homeowners all bump into it daily — and small mistakes compound fast.

The most expensive unit-conversion mistake in history is probably NASA's 1999 Mars Climate Orbiter: a $327 million spacecraft that disintegrated in the Martian atmosphere because one team used pound-force seconds while another expected newton-seconds for impulse data. The probe flew too close to the planet and was lost. NASA's post-mortem cited the unit mismatch as the root cause.

Closer to ground level: prescription dosing errors from mg/kg vs g/kg confusion, recipes that fail when US cups are read as metric, and constant trip-planning headaches when speed limits switch from mph to km/h at borders. Get the conversion right the first time.

Metric vs Imperial Systems

The metric system (formally the International System of Units, or SI) is used by every country in the world except three: the United States, Liberia, and Myanmar. The UK is technically metric but uses imperial units for road signs, beer, and milk. Canada and Australia officially metricated decades ago but still hear "6 feet tall" in conversation.

Metric's big advantage is that it's base 10 throughout: 1 km = 1,000 m, 1 m = 100 cm, 1 cm = 10 mm, 1 kg = 1,000 g. Conversions within metric are just decimal-point shifts.

Imperial units evolved over centuries from older systems and have no consistent base: 12 inches in a foot, 3 feet in a yard, 5,280 feet in a mile. The US still uses imperial for historical reasons — federal metrication legislation passed in 1975 but compliance was voluntary, road signs and consumer products never crossed over, and the cost of relabelling everything eventually killed the push.

In practice you'll meet both systems regularly: science and medicine are metric everywhere; aviation is mixed (altitude in feet, distance in nautical miles, temperature in Celsius); cooking is wildly inconsistent. The converter handles all common units in both systems plus the awkward edge cases like UK vs US gallons.

Common Unit Conversions Reference

From	To
1 inch	2.54 cm (exact)
1 foot	30.48 cm (exact)
1 yard	0.9144 m (exact)
1 mile	1.609344 km
1 nautical mile	1.852 km (exact)
1 ounce (mass)	28.3495 g
1 pound	0.453592 kg
1 stone	6.35029 kg (= 14 lb)
1 fluid ounce (US)	29.5735 ml
1 cup (US)	236.588 ml
1 gallon (US)	3.78541 L
1 gallon (UK)	4.54609 L
1 mph	1.609344 km/h
1 knot	1.852 km/h (= 1 nm/h)
1 acre	4,046.86 m² (= 0.4047 ha)
1 hectare	10,000 m² (= 2.471 acres)
0 °C	32 °F (water freezes)
100 °C	212 °F (water boils)
37 °C	98.6 °F (body temp)
1 GB (decimal)	1,000 MB / 0.931 GiB

Temperature Conversion Formulas

Temperature is the only category where conversion isn't a simple multiply-and-divide, because it's an interval scale with offsets, not a ratio scale. The three formulas you actually need:

°F = (°C × 9/5) + 32

°C = (°F − 32) × 5/9

K = °C + 273.15

Worked examples:

20 °C → (20 × 9/5) + 32 = 36 + 32 = 68 °F (room temperature)
72 °F → (72 − 32) × 5/9 = 40 × 5/9 ≈ 22.2 °C
0 K → −273.15 °C (absolute zero, the lowest possible temperature)

Quick mental shortcuts: doubling the Celsius value and adding 30 gets you Fahrenheit ±5°. Halving (F − 30) gets you Celsius ±5°. Useful in conversation; the converter does the exact math.

Frequently Asked Questions

+How accurate is this converter?

As accurate as JavaScript's 64-bit floating-point math allows — about 15–16 significant decimal digits. For any everyday measurement (cooking, travel, fitness, engineering up to 6 sig figs) that's more than enough. The converter uses internationally agreed conversion factors, most of which are defined as exact values (1 inch = 2.54 cm exactly, 1 yard = 0.9144 m exactly, etc.).

+Why are some units exact and others approximate?

Imperial-to-metric conversions for length and mass were redefined as exact decimal values in 1959 by international agreement (the Yard and Pound Treaty). Volume conversions are exact too. Some derived quantities — like a pound-force or BTU — depend on slightly different definitions in different industries; the most common values are used.

+What's the difference between US and UK gallons?

The US gallon (≈3.785 L) and the UK / Imperial gallon (≈4.546 L) are different quantities — about 20% apart. The US gallon is based on the 1707 English wine gallon; the Imperial gallon was redefined in 1824 as 10 lb of water at 62 °F. Recipes from a UK cookbook will give wrong results if treated as US gallons. The converter has both as separate units.

+How do I convert temperature between Celsius and Fahrenheit?

Use °F = (°C × 9/5) + 32 for Celsius to Fahrenheit, and °C = (°F − 32) × 5/9 for the reverse. Quick estimate: doubling the Celsius value and adding 30 lands within ±5°F of the right answer for most ambient temperatures.

+What's the difference between mass and weight?

In physics they're different things: mass (kg, g, lb) is the amount of matter; weight (N, lbf) is the gravitational force on that mass. In everyday English we use them interchangeably, and bathroom scales report mass even though they're labelled "weight". This converter uses the everyday meaning — kg, lb, oz, etc. are all treated as mass units.

+Can I convert pressure or energy units?

Not in this version — pressure (Pa, psi, bar, atm), energy (J, kJ, kcal, kWh, BTU), and force (N, lbf, kgf) aren't included to keep the UI focused. They're common requests, so they may come in a later update.

+Is my data private?

Yes. The converter runs entirely in your browser — no values are sent to a server, logged, or tied to analytics. Refresh and the inputs are gone.

+Does this work offline?

Once the page is loaded, yes — the conversion logic is client-side JavaScript with no network dependencies. Subsequent calculations work without a connection.