Tools/Math Tools/Unit Converter

Unit Converter Free Online - Length, Weight, Temp

Free online unit converter for length, weight, and temperature conversions used in school, travel, shipping, and daily calculations.

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About this tool

Unit conversion comes up constantly: a product spec lists a dimension in inches but you work in centimeters, a package weight is quoted in pounds but you need kilograms, or a temperature reading needs to move between Celsius and Fahrenheit. This unit converter online free handles the most common length, weight, and temperature unit pairs without requiring you to memorize conversion factors, works in both directions - metric to imperial and imperial to metric - and shows the exact factor used for the conversion.

This unit converter converts values between common length, weight, and temperature units directly in your browser, showing the converted value, the equivalent in the category's base unit, the reverse conversion rate, and the exact conversion factor - all calculated instantly with no server round-trip.

How to Use Unit Converter

Select Conversion Type

Choose length, weight, or temperature.

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Choose Units

Select the source unit and target unit.

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Enter Value

Add the measurement value you want to convert.

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Get Result

Review the converted value and basic conversion details instantly.

Common Workflows

Convert a Length Measurement

Set Type to Length, choose your From and To units (meter, kilometer, centimeter, millimeter, mile, yard, foot, or inch), and enter the value to convert.

Convert a Weight Measurement

Set Type to Weight, choose from kilogram, gram, pound, ounce, or ton (metric tonne), and enter the value.

Convert a Temperature

Set Type to Temperature and choose Celsius, Fahrenheit, or Kelvin for both From and To.

Check the Conversion Factor Being Used

Read the Conversion metric to see the exact factor applied for length and weight conversions - useful when you need to show your work or double-check the math.

Read a Conversion in Reverse

Swap the From and To units, or read the "1 Target in Source" figure, to see the conversion in the opposite direction without re-entering the value.

Best For

Converts between 8 length units, 5 weight units, and the 3 temperature scales (Celsius, Fahrenheit, Kelvin) - it isn't a general-purpose converter for other measurement types like volume, area, or speed.
Works in both directions - pick any unit as the source or target - and shows the exact conversion factor alongside the converted value.
Every conversion is calculated locally in your browser using fixed formulas - no data is sent to a server.

Examples

Convert miles to kilometers

Input

Type Length, From mile, To kilometer, Value 5

Result

Converted Value 8.046720, Base Value 8,046.720000, 1 Target in Source 0.621371, Conversion "1 mile = 1.609344 kilometer"

Base Value shows the entered value expressed in the category's base unit (meters for length); 1 Target in Source shows how many miles equal 1 kilometer, the reverse of the main conversion.

Convert Celsius to Fahrenheit

Input

Type Temperature, From celsius, To fahrenheit, Value 100

Result

Converted Value 212.0000, Base Value 100.0000, 1 Target in Source -17.2222, Conversion "celsius -> fahrenheit"

For temperature, the Conversion field shows only the direction of the conversion, not a numeric factor - the formula used is the standard F = C x 9/5 + 32.

Use Cases

Converting a product dimension for a spec sheet

Convert a measurement from inches to centimeters (or the reverse) to match a specification format.

Converting a shipping or package weight

Convert a weight between kilograms, pounds, grams, or ounces to match a carrier's or supplier's required unit.

Converting a temperature reading

Convert between Celsius, Fahrenheit, and Kelvin for weather or general reference.

Common Mistakes

Problem

Expecting a recipe or ingredient-volume conversion

Solution

There's no cup, tablespoon, or other volume unit - the Weight category converts kilograms, grams, pounds, ounces, and metric tons only. Converting a recipe's cup measurement to grams needs an ingredient-specific density, which this tool doesn't calculate.

Problem

Looking for a speed conversion (mph to km/h)

Solution

Speed isn't one of the three supported categories - only Length, Weight, and Temperature are available.

Problem

Expecting clothing-size conversion

Solution

This is a measurement-unit converter, not a size-chart tool - there's no clothing or shoe size conversion between international sizing systems.

Problem

Assuming "ton" means a US short ton or UK long ton

Solution

The Weight category's "ton" is the metric tonne (1,000 kg) - it isn't the same as a US short ton (about 907 kg) or a UK long ton (about 1,016 kg).

Tips & Best Practices

Check the Conversion metric for the exact factor used

For length and weight, the Conversion field shows the precise factor (like "1 mile = 1.609344 kilometer") - use it if you need to show your work or verify the math independently.

Use "1 Target in Source" to read the reverse conversion instantly

This figure shows how many of the From unit equal one To unit, without needing to swap the dropdowns and re-enter your value.

Double-check "ton" against your context

If your source uses US short tons or UK long tons, convert through pounds or kilograms manually rather than relying on the Weight category's metric-tonne "ton" value.

For a cup-to-gram conversion, use an ingredient-specific reference instead

Volume-to-weight conversion depends on the ingredient's density, so a fixed-factor unit converter (including this one) can't calculate it - look up the specific ingredient's conversion instead.

Limitations

Only three conversion categories

Length, Weight, and Temperature are the only supported types - there's no volume, area, speed, data, pressure, or energy conversion.

No recipe or ingredient volume-to-weight conversion

There's no cup or other volume unit, so converting a recipe measurement (like cups) to a weight (like grams) isn't supported - that conversion depends on the specific ingredient's density, which a fixed-factor unit converter can't calculate.

No speed conversion

Units like mph and km/h aren't available in any category.

No clothing or shoe size conversion

This tool converts measurement units, not size-chart values - there's no clothing or shoe size conversion between regional sizing systems.

"Ton" is the metric tonne only

The Weight category's ton equals 1,000 kg - it doesn't offer the US short ton or UK long ton as separate options.

Fixed decimal precision, not simplified for round numbers

Length and weight results always show 6 decimal places and temperature results show 4, even for a clean result - for example, converting 1,000 meters to kilometers displays as "1.000000" rather than "1".

No validation against negative length or weight values

A negative number is accepted and converted directly (for example, -5 meters converts to -0.005 kilometers) rather than being flagged, even though negative length or weight isn't physically meaningful.

Comparisons

Converted Value vs Base Value vs "1 Target in Source": Reading All Three Together

All three figures come from the same conversion - each answers a different question about it.

	Converted Value / Conversion	Base Value / 1 Target in Source
What it shows	Your entered value in the To unit, and the exact factor used to get there	Your entered value in the category's base unit, and how many From units equal one To unit
Best for	Reading the direct answer to your conversion	Cross-checking the math or reading the conversion in reverse
Same underlying conversion?	Yes - both come from the same Type, From, To, and Value inputs	Yes - both come from the same Type, From, To, and Value inputs

Which should you use?

Use Converted Value for the direct answer, and Base Value or "1 Target in Source" when you need to verify the math or work in the opposite direction.

FAQs

The most useful thing to know before converting: this tool covers length, weight, and temperature only - there's no volume, area, speed, or clothing-size conversion here. Every result is calculated locally in your browser using fixed factors, with the exact factor shown alongside the converted value.