Unit Converter — Length, Weight, Temp Free

Unit Converter

Unit Converter translates between metric and imperial units for length, weight and temperature — the three conversions people need constantly: recipe weights, running distances, weather temperatures, shipping dimensions.

Temperature uses proper conversion formulas (not simple ratios), and results are formatted sensibly whether they’re huge or tiny.

How to use the unit converter

1. Pick a category: length, weight or temperature.
2. Enter the value and choose the from and to units.
3. Read the instant result — it updates as you type.
4. Use ⇄ Swap to flip the conversion direction.

Key features

• 17 units: mm to miles, mg to tonnes, °C/°F/K.
• Live results: updates instantly with every keystroke.
• Correct temperature math: proper °C↔°F↔K formulas.
• Smart formatting: clean numbers, scientific notation only when needed.

Frequently asked questions

How do I convert Celsius to Fahrenheit?

Select temperature, enter your °C value, and convert to °F. The formula is (°C × 9/5) + 32 — the tool does it instantly.

Why is temperature conversion special?

Unlike length or weight, temperature scales have different zero points, so you can’t just multiply by a ratio — the tool applies the correct offset formulas.

How many feet are in a meter?

Exactly 3.28084 feet per meter. The converter uses precise international definitions for every unit.

Does it work offline?

Once the page is loaded, conversions run entirely in your browser with no network needed.

Pro Tips

• Cooking conversions: switch between metric and US cups/spoons instantly when following international recipes.
• DIY & travel: convert miles to kilometers, inches to centimeters, and Fahrenheit to Celsius on the go.
• Double-check critical figures (medication, engineering) against a second source — this tool is for everyday convenience.

More FAQs

How accurate are the conversions?

Conversions use standard international factors and are accurate to typical display precision — plenty for daily life, cooking, travel, and schoolwork.

Does it work offline?

Once the page has loaded, conversions run entirely in your browser with no further network requests.

How It Works: Under the Hood

Most unit conversions are linear transformations: multiply by a factor, optionally add an offset. Length, mass, volume, and data units all convert via a single multiplication — 1 inch is exactly 2.54 cm by international definition, 1 kg is exactly 2.20462262185 lb. The converter stores each unit’s factor relative to a base unit (meters, kilograms, bytes) and converts through it: inches → meters → centimeters. This hub-and-spoke design means N units need only N factors, not N² pairwise rates.

Temperature is the exception — it needs an offset, not just a factor: °F = °C × 9/5 + 32, and Kelvin adds 273.15. Getting the order wrong (adding before multiplying) is the classic implementation bug. Area and volume square or cube the linear factor — 1 m² isn’t 100 cm², it’s 10,000 — another frequent error in naive converters.

Precision handling matters: conversion factors are stored at full double precision, but display rounding is separate. Showing 2.5400000001 cm for 1 inch would be technically honest and practically useless — the converter rounds display output while keeping full precision internally so chained conversions don’t accumulate visible error.

Real-World Use Cases

• Following international recipes: a baker converts a French recipe’s 250g flour to US cups — and learns the hard way that grams-to-cups needs the ingredient’s density (flour ≈ 120g/cup), which is why weight-based recipes are superior.
• Buying furniture abroad: a buyer checks whether a 180cm sofa fits a 72-inch alcove — converting both to one system before ordering avoids an expensive return.
• Engineering homework: a student converts 45 mph to m/s for a physics problem, then double-checks by converting back — catching the factor-of-2.237 error that would have tanked the answer.
• Travel planning: a driver in the US rents a car in Europe and converts the 130 km/h speed limit to ~81 mph, calibrating their instincts before hitting the autobahn.
• Fitness tracking: a runner converts their 5K time from min/km to min/mile to compare against American training plans without mental math mid-run.

Advanced Tips

• Convert to SI first for sanity checks: when a result looks wrong, convert both ends to meters/kilograms/seconds. If the SI numbers don’t make sense, the error is in your input, not the tool.
• Watch significant figures: converting “about 5 miles” to 8.04672 km implies precision you don’t have. Round to match your input’s certainty — “≈8 km” is more honest than six decimals.
• Memorize the survival set: 1 in = 2.54 cm, 1 kg ≈ 2.2 lb, 1 mile ≈ 1.6 km, °F = °C×1.8+32, 1 gal ≈ 3.8 L. These five cover 90% of daily conversions without any tool.
• Distinguish US vs imperial gallons: a US gallon is 3.785 L; an imperial gallon is 4.546 L — a 20% difference that matters enormously for fuel-economy comparisons across the Atlantic.

Common Mistakes to Avoid

• Converting temperature with multiplication only: 20°C isn’t “20 × 1.8 = 36°F” — it’s 68°F. Forgetting the +32 offset is the single most common temperature error.
• Mixing weight and volume for ingredients: 250 ml of flour ≠ 250 g of flour. Volume-to-weight conversion needs density — the converter can’t know your ingredient, so use a kitchen scale for baking.
• Assuming “ounce” means one thing: fluid ounces (volume) vs ounces (weight) are completely different units that happen to share a name. Converting between them without density is meaningless.
• Chaining conversions through rounded displays: converting A→B (rounded display), then typing the rounded B into B→C, compounds rounding error. Convert directly A→C in one step whenever possible.

Everyday Conversions, Solved in Seconds

Three situations cover most unit math: the kitchen (grams to ounces when a recipe crosses the Atlantic), travel (miles to kilometers, Fahrenheit to Celsius on a foreign weather app), and shipping or DIY (inches to centimeters for furniture that must fit through a door). Pick the category, type the value, and the result updates with every keystroke — the swap button flips the direction when you need the reverse. No tables to memorize, no mental arithmetic. Converting money instead of measurements? The currency converter handles live exchange rates.

Precision: When to Trust It and When to Double-Check

Conversions here use standard international definitions — an inch is exactly 2.54 cm — so results are accurate to typical display precision, plenty for cooking, travel, and schoolwork. But precision is not the same as fitness for purpose: medication doses, engineering tolerances, and regulatory filings deserve a second source and the official reference standard. Smart formatting keeps huge and tiny results readable, switching to scientific notation only when needed. For web design sizes, the px to rem converter speaks CSS units.