Convert Units Across Common Measurement Categories
Convert length, area, volume, mass, temperature, time, speed, pressure, force, energy, power, angles and digital data. Every source and target unit stays explicit, including US versus Imperial volume and decimal versus binary storage.
Reviewed: August 2, 2026- 14 compatible categories
- Metric, US and Imperial units
- Exact decimal-rational engine
- Absolute-temperature safeguards
Convert a Measurement
Choose one quantity category, enter a signed decimal or scientific-notation value, then select compatible source and target units.
Choose compatible units and select Convert.
Equivalent units
Every row uses the same stored input, not a rounded result from another row.
| Unit | Symbol | Equivalent value |
|---|---|---|
| — | — | Convert to view equivalents |
Calculation steps
- Select one quantity category and two compatible units.
- The calculator will normalize the value before conversion.
A unit conversion changes how a quantity is expressed. It does not improve the accuracy of the original measurement.
How to Use This Unit Conversion Calculator
Allow about two minutes for one conversion, including a quick check of the unit definition and rounding.
- Choose the quantity category. Select length, area, volume, mass, temperature, time, speed, pressure, force, energy, power, angle or digital data.
- Enter the value. Use a complete decimal or scientific-notation value without commas, expressions or unit symbols.
- Select the source unit. Check the full name, including US, Imperial, avoirdupois, troy, decimal or binary where shown.
- Select the target unit. The list contains only units compatible with the selected quantity.
- Choose display precision. Use enough significant digits for the original measurement and intended purpose.
- Convert and review the steps. Check the base-unit equivalent, one-unit relationship and full equivalent-unit table.
- Confirm context before using the result. Verify the unit definition, measurement uncertainty and rules required for technical, trade, health or legal work.
Unit Conversion Formula
Most supported categories use a linear factor. Each unit stores a factor relative to one base unit. The calculator multiplies by the source factor and divides by the target factor in one exact rational calculation.
For example, the international inch equals exactly 0.0254 metre and the centimetre equals exactly 0.01 metre. Therefore:
Area and volume units use squared and cubed relationships. One square foot equals 0.3048² square metre, while one cubic foot equals 0.3048³ cubic metre. Applying the linear foot factor only once would be wrong.
Temperature uses an offset
Absolute temperature is affine rather than purely multiplicative. The calculator converts through kelvin with these exact scale relationships:
Temperature intervals do not use the offsets. One kelvin interval equals one Celsius-degree interval, while one Fahrenheit- or Rankine-degree interval equals 5/9 kelvin.
Supported Conversion Categories
| Category | Calculation basis | Examples |
|---|---|---|
| Length | metre | nm, µm, mm, cm, km, in, ft, yd, mi, nmi |
| Area | square metre | cm², km², ft², acre, hectare, mi² |
| Volume and capacity | cubic metre | mL, L, ft³, US gal, Imperial gal, fluid ounces |
| Mass | kilogram | mg, g, tonne, lb, oz, stone, short ton, troy oz |
| Absolute temperature | kelvin | °C, °F, K, °R |
| Temperature interval | kelvin interval | Δ°C, Δ°F, ΔK, Δ°R |
| Time | second | ns, µs, ms, min, h, day, week, Julian year |
| Speed | metre per second | km/h, ft/s, mph, knot |
| Pressure | pascal | kPa, bar, atm, psi, Torr, conventional mmHg |
| Force | newton | kN, dyne, kilogram-force, pound-force |
| Energy and work | joule | kWh, calorie, BtuIT, ft·lbf, eV |
| Power | watt | kW, mechanical hp, metric hp, BtuIT/h |
| Plane angle | radian | degree, gradian, turn, arcminute, arcsecond |
| Digital data | bit | MB, GB, KiB, MiB, GiB, TiB |
Worked Conversion Examples
US and Imperial gallons to litres
One US liquid gallon equals exactly 3.785411784 L. One Imperial gallon equals exactly 4.54609 L. The names sound similar, but the units are different. Choose the labelled system instead of entering an unqualified “gallon.”
Fahrenheit to Celsius
For 100 °F, first convert to kelvin: (100 + 459.67) × 5/9 ≈ 310.92778 K. Subtract 273.15 to obtain approximately 37.777778 °C. The calculator carries the exact rational result and rounds only the displayed decimal.
Decimal gigabytes to binary gibibytes
One GB equals 1,000,000,000 bytes. One GiB equals 1,073,741,824 bytes. Therefore, 1 GB is approximately 0.93132257 GiB. Capital B means byte, while lowercase b means bit.
Degrees to radians
A half turn is 180 degrees or π radians. A decimal radian output is approximate because π is irrational. Degree-to-turn or degree-to-arcminute relationships remain rational and can be exact.
Metric, US Customary and Imperial Units
SI prefixes represent powers of ten. One kilometre is 10³ metres and one millimetre is 10⁻³ metre. For data, one kB is 1000 bytes and one MB is 1,000,000 bytes.
US customary and Imperial units share some names but not all definitions. A US liquid gallon contains 128 US fluid ounces. An Imperial gallon contains 160 Imperial fluid ounces. The Imperial gallon is larger, but the Imperial fluid ounce is slightly smaller than the US fluid ounce.
The US customary cup equals exactly 236.5882365 mL. The separate 240 mL unit in this calculator is labelled US nutrition-label cup because that value applies to US food-labelling rules, not to the customary cup.
Mass labels also matter. The ordinary ounce in this tool is the avoirdupois ounce, equal to one-sixteenth pound. A troy ounce is a different mass used for precious metals. Metric tonne, US short ton and Imperial long ton are listed separately.
Absolute Temperature Versus Temperature Difference
A temperature and a temperature change use different equations. Ten degrees Celsius is 50 degrees Fahrenheit because the scale origins differ. A temperature increase of 10 Celsius degrees equals an increase of 18 Fahrenheit degrees because intervals use only the 9/5 scale ratio.
The Absolute temperature category rejects any value below 0 K, −273.15 °C, −459.67 °F or 0 °R. Exactly 0 K is accepted as the scale boundary. The calculator does not assess whether a stated physical temperature is experimentally attainable.
Precision, Exact Factors and Rounding
The arithmetic engine stores entered decimals and defined factors as ratios of integers. This preserves values such as 1e−400 and 1e400 without JavaScript Infinity, underflow or a false zero. It also prevents a multiply-then-divide conversion from overflowing at an unsafe intermediate stage.
An exact conversion factor does not make an original measurement exact. If a length was measured as 12.3 cm, displaying many extra digits after conversion does not add information. Choose significant digits appropriate to the input uncertainty, carry full precision during calculation and round once at the end.
The result uses an equals sign only when the displayed decimal exactly represents the stored result under the selected factor basis. It uses an approximately sign when display rounding, a published approximate factor or a nonzero π-based decimal is involved. The conventional millimetre-of-mercury factor is therefore always identified as approximate when it changes units.
Conversions That Need More Context
This tool converts compatible quantities only. Grams cannot become millilitres without a material density or concentration. Distance cannot become steps without stride length. Currency requires a dated exchange rate and fees. Fuel economy such as miles per gallon versus litres per 100 kilometres uses a reciprocal relationship, not one linear factor.
Calendar months have variable lengths, so they are not included as fixed time units. The listed Julian year is explicitly 365.25 days, not a promise about a civil calendar interval. Pressure conversion does not change gauge pressure into absolute pressure because that requires a reference atmospheric pressure.
Common Unit Conversion Mistakes
- Using a linear factor for area or volume. Square and cube the length relationship.
- Mixing US and Imperial liquid units. Select the complete unit name.
- Confusing mass ounces with fluid ounces. They measure different quantities.
- Applying temperature offsets to intervals. Use the separate Temperature interval category.
- Treating GB as GiB. Decimal and binary prefixes use different powers.
- Rounding an intermediate result. Convert from the stored input and round only the final display.
- Assuming unit conversion validates a measurement. Calibration, uncertainty and context remain separate questions.
Related Calculators
Use focused tools when the relationship needs more than one conversion factor. Browse the full Unit Conversion & Measurement Calculators directory for the complete cluster.
Frequently Asked Questions
These answers clarify unit definitions, temperature handling and display precision.
How does the unit conversion calculator work?
For linear units, it multiplies the entered value by the source unit’s base factor and divides by the target unit’s factor. Absolute temperature uses scale-specific offsets and ratios instead.
Are all conversion factors exact?
No. Many defined relationships are exact, including the international inch, pound, US liquid gallon and Imperial gallon. Some published factors are conventional or rounded, and decimal angle results involving π are approximate.
Why are US and Imperial gallons separate?
They have different volumes. One US liquid gallon equals exactly 3.785411784 litres, while one Imperial gallon equals exactly 4.54609 litres.
Can I convert grams directly to millilitres?
Not with one fixed factor. Grams measure mass and millilitres measure volume. Their relationship requires the material’s density or a valid concentration under stated conditions.
What is the difference between absolute temperature and a temperature interval?
An absolute temperature uses scale offsets, while an interval uses only a scale ratio. Ten degrees Celsius is 50 degrees Fahrenheit, but a 10 Celsius-degree increase equals an 18 Fahrenheit-degree increase.
Does the calculator accept negative values and zero?
Yes. Signed values and zero are valid for mathematical unit conversion. Absolute-temperature inputs are the exception: values below 0 K are rejected.
Why are MB and MiB different?
MB uses the decimal SI prefix: one MB is 1,000,000 bytes. MiB uses the IEC binary prefix: one MiB is 1,048,576 bytes. Lowercase b means bit and uppercase B means byte.
How many significant digits should I use?
Use enough working precision to avoid premature rounding, then report only the precision justified by the original measurement and its purpose. Extra displayed digits do not add measurement accuracy.
Why does swapping units show a rounded value in the input?
The input box shows a readable decimal, but the calculator keeps the exact internal rational result until you edit the value. Swapping back therefore does not reuse the rounded display.
Can this result replace a calibrated measurement or official conversion?
No. Confirm the applicable unit definition, instrument calibration, uncertainty, rounding rule and governing standard for trade, laboratory, engineering, health, legal or safety decisions.
Method and Review Basis
- BIPM SI Brochure, 9th edition, current SI units, prefixes and temperature relationships.
- NIST Unit Conversion guidance, conversion procedure, significant digits and round-last practice.
- NIST SP 811 Appendix B.9, conversion factors by kind of quantity.
- NIST SI Temperature guidance, exact Celsius, Fahrenheit and interval relationships.
- NIST Binary Prefixes, decimal SI versus IEC binary data units.
- NIST Handbook 44, 2026 Appendix C, current general tables of measurement units.
- 21 CFR 101.9, the 240 mL US nutrition-labelling cup.
Measurement disclaimer: This calculator converts the numerical values you enter. It does not certify a measurement, instrument, material property, exchange rate, dose, engineering specification or legal-metrology result. Confirm unit definitions, conditions, uncertainty, rounding and the applicable authority before relying on a conversion for trade, laboratory, health, engineering, legal or safety work.