Common Unit Conversion FAQs

Last updated: July 2025

Quick answers to frequent questions about converting units, using tounits.com, and avoiding common mix-ups between US customary, imperial, and metric measures.

How do I convert on tounits.com?

Type a number and unit in the search box (e.g. 5 feet, 100 kg, 72 F). Results appear instantly. You can also pick an input unit from the dropdown and type just a number. Shareable URLs encode your query so you can bookmark or send a link.

Which units are supported?

We support length, mass, temperature, volume, area, time, speed, pressure, and more—including metric, US customary, and imperial variants. Use the unit selector or type the unit name (e.g. “inch”, “liter”, “celsius”) after your number. Where US and UK units differ (gallons, pints), both are available.

Is the conversion accurate?

We use standard conversion factors aligned with NIST and BIPM definitions (e.g. 1 inch = 2.54 cm exactly; 1 lb = 0.45359237 kg). Results are suitable for general reference, travel, cooking, and education. For critical applications (engineering, medicine, legal), verify with an authoritative source and carry units through your calculations explicitly.

What’s the difference between US and UK gallons?

1 US gallon ≈ 3.785 L; 1 UK (imperial) gallon ≈ 4.546 L. They are not interchangeable—a British “gallon” is about 20% larger. Choose the correct unit in the converter when converting gallons. See our US vs UK units guide for pints and tons too.

Why do I see “ounce” and “fluid ounce”?

Ounce (oz) is mass; fluid ounce (fl oz) is volume. They are not interchangeable. Use oz for weight (e.g. 4 oz cheese) and fl oz for liquids (e.g. 8 fl oz water). Confusing the two is a common recipe and shipping error.

Can I use tounits offline?

After you’ve visited once, the app can work offline so you can convert without internet. Results use the same factors as when online. Theme and recent queries are stored locally in your browser.

Do you store my conversions?

We only store your recent queries and theme preference in your browser (local storage). We don’t send that data to our servers for basic conversion. With your consent, privacy-focused analytics (Matomo) may record anonymized page views. See our Privacy Policy.

How do I switch between Celsius and Fahrenheit?

Enter a value with the scale (e.g. 100 F or 37 C). The converter shows both and Kelvin where relevant. Formulas: °F = (°C × 9/5) + 32; °C = (°F − 32) × 5/9.

Why does my recipe conversion look wrong?

Volume-to-weight conversions depend on the ingredient—a cup of flour is not the same grams as a cup of sugar. For baking, prefer weight (grams) on a kitchen scale. Our cooking conversions guide lists common cup-to-gram values.

What are SI prefixes (kilo, milli, etc.)?

Metric prefixes scale base units by powers of ten: kilo- (×1,000), centi- (÷100), milli- (÷1,000), micro- (÷1,000,000). So 5 km = 5,000 m and 500 mg = 0.5 g. See the SI prefixes guide for a full table.

Is metric the same as SI?

SI (International System of Units) is the modern metric system used in science, with precisely defined base units. Everyday “metric” measures like liters and kilograms are compatible with SI. The US uses SI in federal science and many industries but customary units in daily life.

How do I report an error?

Email [email protected] with the page URL, the units involved, and a reference source if possible. We review correction requests regularly.

Try a conversion now on the tounits.com converter.