Best Free Unit Converters

BY TOOLS.FUN · MARCH 28, 2026 · 4 min read

Unit conversion comes up constantly — cooking recipes in cups vs. grams, international shipping in pounds vs. kilograms, or server specs in GB vs. GiB. The best free converters give you instant results without ads or confusion. Here is what works.

converters.now — All Units in One Place

converters.now covers length, weight, temperature, volume, area, speed, data storage, and time. Select the category, pick source and target units from dropdowns, type a number, and the result appears instantly. No page reloads, no ads, and the URL updates to reflect your conversion — so you can bookmark frequently used conversions.

The tool handles edge cases well: it correctly distinguishes between gigabytes (1000-based) and gibibytes (1024-based), which matters when comparing hard drive specs to RAM sizes.

Google Conversions — Built Into Search

Type "150 lbs in kg" or "72 fahrenheit to celsius" into Google and the answer appears above the search results. The widget lets you change units after the fact and shows a small calculator. For one-off conversions when you are already in the browser, nothing is faster.

Google also handles currency conversions with live exchange rates, cooking measurements, and obscure units like nautical miles and troy ounces. The limitation is that you cannot bookmark a specific conversion or do batch conversions.

Tip: For developers working with data units, remember the difference between decimal (SI) and binary (IEC) prefixes. 1 GB = 1,000,000,000 bytes (decimal), but 1 GiB = 1,073,741,824 bytes (binary). Operating systems mix these inconsistently, which is why your "500 GB" drive shows as ~465 GB in Windows.

Metric vs. Imperial — A Quick Reference

The most common conversions people search for are: kilometres to miles (multiply by 0.621), kilograms to pounds (multiply by 2.205), Celsius to Fahrenheit (multiply by 1.8, add 32), and litres to gallons (multiply by 0.264 for US gallons). If you do these frequently, memorizing the multipliers is faster than any tool.

Specialized Converters Worth Knowing

Cooking: For recipe conversions, King Arthur Baking's ingredient weight chart is more accurate than generic volume-to-weight converters because different ingredients have different densities.

Typography: Points to pixels (1pt ≈ 1.333px at 96 DPI) matters for CSS work. The Color Converter on tools.fun handles colour unit conversions (HEX to RGB to HSL), which is the typography-adjacent conversion developers need most often.

Time zones: Not technically a unit conversion, but converting between time zones is a daily task for remote teams. Use a world clock tool rather than doing UTC offset math in your head.

Developer tip: When building applications that handle units, always store values in a base unit (metres, grams, seconds) and convert only at the display layer. This prevents rounding errors from accumulating through multiple conversions and makes your data consistent across locales.

Offline Conversion

If you need unit conversion without internet access, most smartphone calculators include a unit converter. On macOS, Spotlight (Cmd+Space) handles basic conversions natively — type "5 miles in km" and the answer appears. On Windows, the built-in Calculator app has a converter mode accessible from the hamburger menu.

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