Math

Unit Converter — Length, Weight, Volume & Temperature

Instantly convert miles to km, kg to lb, °C to °F, gallons to liters and 20+ more units. Exact international factors — no rounding, no sign-up. Includes quick-reference tables.

National Institute of Standards and Technology data · June 2026
Edited by Martín Rodríguez
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Edited by: Martín Rodríguez (editorial policy )

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Miles to Kilometers Converter (+ km to miles)Convert miles to kilometers instantly. 1 mile = 1.609344 km exactly (NIST). Works both ways. Includes reference table for common running, driving, and cycling distances.Gallons to Liters Converter (US & UK gallon)1 US gallon = 3.78541 L | 1 UK gallon = 4.54609 L. Convert gallons to liters instantly using the exact NIST factor. Includes quick-reference table and US vs UK gallon comparison.Celsius to Fahrenheit & Kelvin ConverterConvert Celsius to Fahrenheit (and back) instantly. °F = °C × 1.8 + 32. Quick reference: 0°C = 32°F · 37°C = 98.6°F · 100°C = 212°F. Free, no signup.Cylinder Volume Calculator (V = π·r²·h)Calculate cylinder volume instantly with V = π·r²·h. Enter radius and height to get volume in cm³, liters, and surface area. Reference table included.

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How to use this calculator

Follow this tool’s steps, then review its formula, assumptions, and limits below.

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Tap the Calculate button

Check the result

Convert between metric and imperial units for length, weight, volume, and temperature using exact internationally-defined factors (1 inch = 2.54 cm exactly, 1 lb = 0.45359237 kg exactly). Pick a unit to convert from and to — the converter keeps you within the same dimension and tells you if you try to mix, say, mass and length.

When to use this calculator

Converting miles to kilometers (or back) for travel and running
Switching a recipe between US cups/ounces and metric ml/grams
Converting body weight between kilograms and pounds
Reading a thermostat or recipe in the other temperature scale
Converting heights and distances between feet/inches and centimeters
Checking a product spec given in unfamiliar units

Key Exact Conversion Factors by Dimension

Unit	Exact Equivalent	Dimension
1 inch	2.54 cm (exact)	Length
1 foot	0.3048 m (exact)	Length
1 yard	0.9144 m (exact)	Length
1 mile	1,609.344 m (exact)	Length
1 pound (lb)	0.45359237 kg (exact)	Mass
1 ounce (oz)	28.349523 g (exact)	Mass
1 US gallon	3.785412 L	Volume
1 US cup	236.588 mL	Volume
°F = °C × 9/5 + 32	°C = (°F − 32) × 5/9	Temperature

Fuente: NIST — National Institute of Standards and Technology, NIST Handbook 44 & BIPM International System of Units (2026)

How it works

How to Convert Units

Enter a value, pick what you're converting from and to, then press Calculate. The converter handles length, weight (mass), volume, and temperature — all using exact internationally-defined factors.

Miles ↔ Kilometers Table

Miles (mi)	Kilometers (km)
1	1.6093
3	4.8280
5	8.0467
10	16.0934
26.2 (marathon)	42.195
100	160.934

Formula: km = mi × 1.609344

Kilograms ↔ Pounds Table

Kilograms (kg)	Pounds (lb)
1	2.2046
5	11.0231
10	22.0462
50	110.231
70	154.324
100	220.462

Formula: lb = kg × 2.204623 — or — kg = lb × 0.453592

Celsius ↔ Fahrenheit Table

Celsius (°C)	Fahrenheit (°F)
−40	−40 (same!)
0	32 (freezing)
20	68 (room temp)
37	98.6 (body temp)
100	212 (boiling)

Formula: °F = °C × 9/5 + 32 — or — °C = (°F − 32) × 5/9

US Gallons ↔ Liters Table

US Gallons (gal)	Liters (L)
1	3.7854
5	18.927
10	37.854
20	75.708
50	189.271

Formula: L = gal × 3.785412

Key Exact Factors (by international definition)

1 inch  = 2.54 cm        (exact)
1 foot  = 0.3048 m       (exact)
1 mile  = 1609.344 m     (exact)
1 yard  = 0.9144 m       (exact)
1 pound = 0.45359237 kg  (exact)
1 oz    = 28.349523 g    (exact)
1 US gal = 3.785412 L
1 US cup = 236.588 mL

How It Works Internally

For length, mass, and volume: every unit has a factor to a base unit (meter / kilogram / liter). The result is: result = value × fromFactor ÷ toFactor. Temperature uses offset formulas because the scales don't share a zero point.

Limitations

You can only convert within the same physical dimension (mass, length, or volume).

US and UK gallons differ (UK gallon = 4.546 L); this converter uses US liquid measures.

Volume ↔ weight conversions (e.g. cups to grams for flour) depend on density and are not supported here.

Example: convert 5 miles to kilometers

Exact factor: 1 mile = 1.609344 km by international definition.

Multiply: 5 × 1.609344 = 8.04672 km.

5 miles = 8.04672 kilometers

Figures use exact internationally-defined factors.

Frequently asked questions

How many kilometers is a mile?

1 mile equals exactly 1.609344 kilometers (this is an exact international definition). To convert miles to km, multiply by 1.609344. Example: 5 miles = 8.047 km; 26.2 miles (a marathon) = 42.195 km. Going the other way: 1 km = 0.621371 miles.

How do I convert kg to pounds?

Multiply kilograms by 2.204623 to get pounds. Example: 70 kg = 154.32 lb. To convert pounds to kg, multiply by 0.453592. Example: 150 lb = 68.04 kg. The exact definition is 1 lb = 0.45359237 kg.

How do I convert Celsius to Fahrenheit?

Multiply by 9/5 then add 32: F = C × 1.8 + 32. Example: 100 °C = 212 °F (water boils), 0 °C = 32 °F (water freezes), 37 °C = 98.6 °F (body temperature). To reverse: C = (F − 32) × 5/9.

How many liters in a gallon?

One US gallon = 3.785412 liters. Note: the UK (imperial) gallon is larger at 4.546092 liters — about 20% more. This converter uses US gallons throughout. So 5 US gallons = 18.927 liters.

How do I convert inches to centimeters?

Multiply inches by 2.54 (this is exact by definition). Example: 6 inches = 15.24 cm; 12 inches (1 foot) = 30.48 cm. To go the other way: cm ÷ 2.54 = inches.

Are US and UK gallons the same?

No. A US gallon is 3.785412 liters; an imperial (UK) gallon is 4.546092 liters — about 20% larger. This converter uses US liquid measures for gallons, quarts, pints, cups, and fluid ounces. If you need UK measures, note that 1 UK pint = 568 mL, not 473 mL.

Why can't I convert kilograms to meters?

Because they measure different physical dimensions — mass versus length. You can only convert within the same dimension. If you try to mix dimensions, the calculator returns an error message instead of a meaningless number.

How do I convert feet and inches to centimeters?

First convert everything to inches (feet × 12 + remaining inches), then multiply by 2.54. Example: 5 feet 10 inches = 70 inches = 177.8 cm. Use this calculator by entering the total inches in the value field and selecting 'inches → centimeters'.

How do I convert cups to milliliters?

1 US cup = 236.588 mL (exactly 236.5882365 mL by definition). So 2 cups = 473.18 mL; 1/2 cup = 118.29 mL. Note: this is a true unit conversion — if you need cups to grams, that depends on the ingredient's density.

How accurate are the results?

Results use exact internationally-defined conversion factors and are shown to up to 6 significant decimal places. For length and mass, the underlying factors are exact (e.g. 1 inch = 2.54 cm with no rounding). For everyday use you can round freely; for engineering work the factors are precise enough.

Sources & references

NIST — Unit Conversion Tables & International System of Units (SI) — National Institute of Standards and Technology (2026)
NIST Handbook 44 — Appendix C: General Tables of Units of Measurement — National Institute of Standards and Technology (2026)
International Bureau of Weights and Measures (BIPM) — The International System of Units — Bureau International des Poids et Mesures (2026)

Methodology & trust

Editorial

Math calculator with its formula verified automatically against NIST — Unit Conversion Tables & International System of Units (SI), per our editorial policy and methodology.

Updates

Updated: June 2026. Parameters are verified periodically against the cited sources.

Privacy

Calculations run 100% in your browser. We do not store or transmit your data.

Limitations

Indicative results. For critical decisions, consult a professional.

📌 How to cite this calculator

APA format

Rodríguez, M. (2026). Unit Converter — Length, Weight, Volume & Temperature. Hacé Cuentas. https://hacecuentas.com/en/unit-converter

BibTeX

@misc{hacecuentas_unit_converter_2026,
  author       = {Rodríguez, Martín},
  title        = {{Unit Converter — Length, Weight, Volume & Temperature}},
  year         = {2026},
  howpublished = {\url{https://hacecuentas.com/en/unit-converter}},
  note         = {Hacé Cuentas}
}

Content licensed under CC-BY 4.0 — reuse it citing the source with a link to Hacé Cuentas.

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Unit Converter — Length, Weight, Volume & Temperature 🌎

How to use this calculator

When to use this calculator

Key Exact Conversion Factors by Dimension

How it works

How to Convert Units

Miles ↔ Kilometers Table

Kilograms ↔ Pounds Table

Celsius ↔ Fahrenheit Table

US Gallons ↔ Liters Table

Key Exact Factors (by international definition)

How It Works Internally

Limitations

Example: convert 5 miles to kilometers

Frequently asked questions

Sources & references

Methodology & trust

Related calculators

Unit Converter — Length, Weight, Volume & Temperature