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What does this converter do?
Convert metric and imperial length, weight, volume, speed, pressure and area by multiplying by the appropriate factor; temperature needs an offset formula. Exact definitions include 1 inch = 2.54 cm, 1 pound = 0.45359237 kg and 1 US gallon = 3.785411784 L. For example, 12 inches x 2.54 = 30.48 cm; Celsius to Fahrenheit uses F = C x 9/5 + 32, so 20 C = 68 F.
- 1 inch = 2.54 cm exactly; 1 foot = 0.3048 m exactly, so 1 m is approximately 3.28084 ft.
- 1 mile = 1.609344 km exactly; the same factor converts mph to km/h.
- 1 pound = 0.45359237 kg exactly; 1 avoirdupois ounce = 28.349523125 g exactly.
- 1 US liquid gallon = 3.785411784 L; 1 imperial gallon = 4.54609 L, both exact definitions.
- F = C x 9/5 + 32, so 20 C = 68 F; temperature is not a factor-only conversion.
- 1 bar = 100000 Pa, approximately 14.503773773 psi; 1 standard atmosphere = 101.325 kPa.
US and imperial gallons: select the liquid measure first
A gallon is not a universal volume. The US liquid gallon is exactly 3.785411784 liters, while the imperial gallon used in UK specifications is exactly 4.54609 liters. Those are different definitions, not alternative rounding choices. A container marked 5 US gal holds 18.92705892 L; a container marked 5 imperial gal holds 22.73045 L. If a product description says only gallons, check its market, label or technical specification before entering a value. This page labels its gallon option as US gallons. The imperial definition is provided here for comparison, not as an interchangeable setting in the converter.
The difference extends to the smaller measures within each system. A US gallon contains 128 US fluid ounces, while an imperial gallon contains 160 imperial fluid ounces. Each fluid ounce also has a different volume: 29.5735295625 mL for US liquid measure versus 28.4130625 mL for imperial measure. A recipe, aquarium specification or fuel figure can therefore be wrong even when its arithmetic looks tidy. Keep the system attached to the unit throughout the calculation, then convert to liters or milliliters as a common reference. US dry measures are a separate convention and should not be substituted for these liquid definitions.
Ounces versus fluid ounces: mass needs density to become volume
An ounce on a kitchen scale and a fluid ounce on a measuring cup describe different quantities. The ordinary avoirdupois ounce is a mass unit, exactly 28.349523125 grams; 16 of these ounces make 1 pound. A US fluid ounce is a volume unit, exactly 29.5735295625 milliliters. The similar names do not create a general conversion between them. Use the weight category for pounds, ounces, kilograms and grams. Use the volume category for liters, milliliters and US fluid ounces. A packaged food can show both net weight and serving volume, so read which quantity the label actually specifies before copying its number.
To move from mass to volume, supply a density for the actual substance and its relevant conditions. Volume equals mass divided by density when the units agree; mass equals volume multiplied by density. Flour, cooking oil and water do not share a density, and a loosely filled scoop of flour can differ from a packed scoop. A generic unit converter cannot infer that missing information from the word ounce. Prefer a scale when a recipe specifies mass, and use a calibrated volume measure when it specifies liquid volume. Precious-metal troy ounces are another mass convention, not the ordinary ounces used by this tool.
Exact factors, rounded displays and squared area conversions
An exact definition and a decimal display are different things. The international foot is exactly 0.3048 meters, so converting meters to feet means dividing by that value. The exact reciprocal is 1250/381, whose decimal expansion does not terminate. Writing 3.28084 feet per meter is convenient but rounded. For 10 meters, the defining calculation gives 32.808398950131... feet, displayed here as 32.8084 feet. Retain the full available intermediate result and round only at the end. Adding decimal places cannot improve the original measurement: a rough tape reading does not become a laboratory measurement merely because the output shows more digits.
Dimensions also determine which factor belongs in a calculation. Length uses the factor directly, area uses its square, and volume uses its cube. Since 1 foot = 0.3048 meters, 1 square foot = 0.09290304 square meters. Converting square feet to linear feet is a different problem that needs a material width; the related calculator handles that input. Temperature readings require another exception: multiplying by 9/5 is insufficient without adding 32 when converting Celsius to Fahrenheit. The tool's precision selector changes displayed decimal places, but some stored coefficients are already rounded. Use exact definitions for auditing and match final precision to the measurement and decision.
How this calculator works
Formula
For units of the same quantity, value_out = value_in x source_coefficient / destination_coefficient, with both coefficients expressed in the same base unit. For meters to feet, divide by 0.3048: 1 m = 1250/381 ft exactly, approximately 3.28084 ft. Miles to kilometers: km = mi x 1.609344. Kilograms to pounds: lb = kg / 0.45359237. Celsius to Fahrenheit: F = C x 9/5 + 32; Fahrenheit to Celsius: C = (F - 32) x 5/9. For area, square the corresponding length factor; for volume, cube it. Thus 1 square foot = 0.09290304 square meters. Speed uses distance per time, so 1 mph = 1.609344 km/h. Pressure examples: 1 bar = 100000 Pa, approximately 14.503773773 psi; 1 standard atmosphere = 101.325 kPa.
Worked example
Length: 10 m / 0.3048 m per foot = 32.808398950131... ft, or 32.8084 ft rounded. A distance of 26.2 mi x 1.609344 km per mile = 42.1648128 km, or 42.16 km rounded; this is a rounded marathon-distance example, not an exact race specification. Mass: 70 kg / 0.45359237 kg per pound = 154.323583529414... lb, or 154.3236 lb rounded. Temperature: 20 C x 9/5 + 32 = 68 F; reversing gives (68 - 32) x 5/9 = 20 C. Volume: 5 US gal x 3.785411784 L per gallon = 18.92705892 L, or 18.93 L rounded. The same numeral in imperial gallons gives 5 x 4.54609 = 22.73045 L, or 22.73 L rounded.
Assumptions to verify
- Length uses the international foot, not the historical US survey foot.
- Weight means mass in kilograms, pounds or avoirdupois ounces, not gravitational force or troy ounces.
- The tool's gallon and fluid-ounce choices are US liquid measures; imperial measures are discussed separately and US dry gallons are excluded.
- Temperature readings require an offset formula, not multiplication alone; a temperature interval is different from an absolute reading.
- Conversion preserves the measured quantity, not the accuracy of the original measurement; round for the source measurement and intended use.
Frequently asked questions
How many centimeters are in an inch?
1 inch is exactly 2.54 centimeters. Multiply inches by 2.54 to get centimeters, or divide centimeters by 2.54 to get inches. For example, 12 x 2.54 = 30.48 cm.
How do I convert kilograms to pounds?
Divide kilograms by 0.45359237, the exact number of kilograms in 1 pound. For example, 70 / 0.45359237 = 154.323583529414... lb, which rounds to 154.3236 lb. Convert pounds to kilograms by multiplying by 0.45359237.
Is a US gallon the same as a UK gallon?
No. A US liquid gallon is exactly 3.785411784 L, while a UK imperial gallon is exactly 4.54609 L. The difference is 0.760678216 L per gallon. The converter's gallon option is US liquid, so do not enter an imperial gallon quantity as though it were US gallons.
How do you convert Celsius to Fahrenheit exactly?
Use F = C x 9/5 + 32. For example, 20 x 9/5 + 32 = 68 F. Reverse it with C = (F - 32) x 5/9. Thus 32 F = 0 C. These formulas convert temperature readings; temperature differences do not use the offset.
What is the difference between oz and fl oz?
An avoirdupois ounce (oz) measures mass: 1 oz = 28.349523125 g exactly. A fluid ounce (fl oz) measures volume: 1 US fl oz = 29.5735295625 mL exactly. You need the substance's density to convert between mass ounces and fluid ounces.
How many feet are in 10 meters?
10 / 0.3048 = 32.808398950131... feet, which rounds to 32.8084 feet. The familiar factor 3.28084 feet per meter is rounded, not exact; use the defining foot length of 0.3048 meters when calculating.
How do I convert mph to km/h?
Multiply miles per hour by 1.609344 because 1 mile is exactly 1.609344 kilometers and the time unit stays the same. Divide km/h by 1.609344 to reverse the conversion.
How do I convert bar to psi?
1 bar equals 100000 pascals and approximately 14.503773773 psi. Multiply bar by that rounded psi factor, or use the converter's pascal-based coefficients. Compare readings on the same gauge or absolute pressure basis; changing units does not change that reference.
Are conversion factors exact, and can I use a length factor for area?
Some defining factors are exact, including 1 inch = 2.54 cm and 1 pound = 0.45359237 kg. Reciprocal decimal factors may be rounded, and browser arithmetic has finite precision. Area needs the squared length factor: 1 square foot = 0.3048 x 0.3048 = 0.09290304 square meters, not 0.3048 square meters. Volume uses the cubed length factor.
Cite this tool
BoringToolsKit. “Unit Converter.” boringtoolskit.com/unit-conv/. Free to reference in articles, syllabi, and answer posts with a link.
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Worked example: carpet roll yards from square yards
The area-length mode converts an area of flooring or fabric into a run length, and it is the only mode that needs a third input: the material width. Take a common carpet order: 40 square yards of material, roll width 12 feet, and you need linear yards. Type square yards as the area unit, linear yards as the length unit, width 12, width unit feet, waste 0.
Internally the tool converts both widths to meters first: 12 ft x 0.3048 = 3.6576 m. The area converts as 40 sq yd x 0.83612736 = 33.4450944 square meters. Run length in meters is 33.4450944 / 3.6576 = 9.144 m, and linear yards is 9.144 / 0.9144 = exactly 10 linear yards. The result panel reads '10 linear yd' and the factor line states the rate at the width you entered: 1 sq yd = 0.25 linear yd at 12 ft width. That rate is width-specific: the same 40 sq yd on a 13.2 ft wide roll (4.02336 m) gives 33.4450944 / 4.02336 / 0.9144 = 9.0909 linear yards.
Now set waste to 10 percent. The computed length stays 10 linear yd, but the output adds a planning line: with 10% waste, buy 11 linear yd, because the tool multiplies the run length by 1 + 10/100 = 1.1. The waste multiplier also applies in the reverse direction: 10 linear yd on a 12 ft roll becomes 40 sq yd of material, and a 10 percent allowance makes it plan for 44 sq yd instead. The formula behind all of it is run_m = area_m2 / (width_m x width_unit_factor_m_per_unit), then divided by the target unit's meter factor 0.9144 for linear yards.
Boundary behavior: zero, caps, negatives, and precision
Several inputs have hard edges worth knowing before you type. Waste accepts 0 to 100 and rejects anything else: a value of -5 or 150 returns 'Waste allowance must be between 0 and 100' instead of a result. At 0 percent the planning value equals the raw value exactly; at the 100 percent cap the planning value is exactly double the raw value, so 10 linear yd becomes 20 linear yd, which is the tool's way of saying order twice the measured run. Material width must be strictly greater than zero: width 0 returns an error, and width 0.0001 is accepted but produces an absurdly large run length, which is arithmetic, not a bug.
Negative values are rejected for every type except temperature, where the input loses its min=0 attribute so -40 F is legal and converts to -40 C. Type mismatches inside area-length fail loudly: picking two square units, or two linear units, returns 'Choose one square-area unit and one linear-length unit.' because no width can bridge them. Same-unit From and To pairs are prevented in the dropdown, which jumps the To selection to the next option.
Precision truncates display, never the math: the default 6 decimals shows 25 m to ft as 82.020997, while precision 2 shows 82.02; the underlying value is always the full 25/0.3048 = 82.0209973753 ft. Displays switch to scientific notation only when a magnitude falls below 10^-precision or above 10^15. Finally, the tool is a pure offline matrix: it has no live exchange-style rates to go stale, but it also will not warn you when a job site uses nominal widths (a '12 foot' roll that measures 11.83 ft) that change the real answer by about 1.4 percent.