Volume Converter
Convert between metric and both US and imperial liquid measures — litres, gallons, cups, fluid ounces and cubic feet — with exactly defined factors.
Volume Converter
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Results are a model, not a quotation — an institution's own figures govern.
- Every input is an assumption; change one and the answer changes with it.
- Rounding is applied only at the display layer, so totals may differ by a cent from a statement that rounds each line.
In short: Volume conversion routes every value through the cubic metre. The US gallon is defined as exactly 231 cubic inches, giving 3.785411784 litres, while the imperial gallon is exactly 4.54609 litres. The two differ by about 20%, which is why US and UK recipes and fuel figures are not interchangeable.
Formula
Every unit is expressed as its exact size in cubic metres; one multiply and one divide completes any pairing without an intermediate rounding step.
Worked Example
- Start from the definition. A US gallon is exactly 231 cubic inches.
- Convert the inch. One cubic inch is 0.0254³ = 0.000016387064 m³.
- Multiply out. 231 × 0.000016387064 = 0.003785411784 m³.
- Convert to litres. × 1,000 gives 3.7854118 L.
- Contrast the imperial gallon. At exactly 4.54609 L it is about 20% larger.
Metrology note. The 20% gap between US and imperial gallons is the single most expensive unit error in everyday use — it distorts fuel-economy comparisons between US and UK figures unless both are converted to litres per 100 km first.
Strengths & Limits Of This Model
Where this engine is strong
- Runs entirely in your browser — no figure you type is transmitted or stored.
- Shows the full working, so every number can be traced and challenged.
- Free, unmetered and free of affiliate incentives.
Where it stops
- Generalised assumptions cannot capture every individual circumstance.
- Jurisdiction-specific rules and mid-year changes may not be reflected.
- A model output is not a substitute for a professional review of your position.
Practical Use Cases
Scaling recipes between US and metric measures
US recipes use volume cups while most of the world weighs ingredients. Converting cups to millilitres is the first step, though for dry ingredients weight remains more reliable — the Recipe Scaling Calculator handles the ingredient-specific cases.
Comparing fuel consumption across markets
US miles per gallon and UK miles per gallon use different gallons, so the same car appears roughly 20% more efficient in UK figures. Convert both to litres per 100 km with the Fuel Cost Calculator before drawing conclusions.
Sizing tanks, pools and containers
Capacity is usually specified in litres or gallons while dimensions are in feet or metres, so a cubic measurement has to be converted before it can be compared. The Concrete Calculator applies the same volumetric logic to poured material.
Methodology & Editorial Standards
All units are stored as exact multiples of the cubic metre. The US liquid gallon derives from its legal definition of 231 cubic inches, which with the exact inch of 0.0254 m gives exactly 0.003785411784 m³; US quarts, pints, cups, fluid ounces, tablespoons and teaspoons are exact binary subdivisions of it. The imperial gallon is exactly 4.54609 litres by the Weights and Measures Act, and the imperial fluid ounce is one hundred and sixtieth of that. The oil barrel is exactly 42 US gallons. All conversion factors are exact by definition under the International System of Units, or exact by international agreement where the unit is defined by treaty. Values are held at full IEEE-754 double precision internally and rounded only for display, so chained conversions do not accumulate drift.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Volume Converter — 20 Expert FAQs
20 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How many millilitres are in a US cup?
Exactly 236.5882365 mL. The US cup is one sixteenth of a US gallon, and since the gallon is exactly 231 cubic inches the result is exact, though it is almost always rounded to 240 mL in nutrition labelling.
Why are US and imperial gallons different?
They come from different legal definitions. The US gallon derives from the old English wine gallon of 231 cubic inches, while the imperial gallon was redefined in 1824 as the volume of ten pounds of water. The imperial gallon is about 20% larger.
How many litres in a US gallon?
Exactly 3.785411784 litres. This follows directly from the definition of 231 cubic inches combined with the exact inch, so it is not an approximation.
Is a fluid ounce a measure of weight?
No. A fluid ounce measures volume; the avoirdupois ounce measures mass. They coincide only for water at particular conditions, and confusing the two is a frequent source of error in recipes and dosing.
How many US fluid ounces are in an imperial fluid ounce?
About 0.96076. The imperial fluid ounce is slightly larger at 28.4130625 mL against the US value of 29.5735295625 mL, even though the imperial gallon is much larger — imperial gallons divide into 160 fluid ounces rather than 128.
What is an oil barrel?
Exactly 42 US gallons, or about 158.987 litres. It is a petroleum industry convention and differs from other barrels used for beer and dry goods, which is why the unit is always qualified in trade documents.
How do I convert cubic feet to gallons?
One cubic foot is exactly 0.028316846592 m³, which is about 7.4805195 US gallons. The conversion is exact in principle since both units derive from the exact inch.
Why do dry and liquid measures differ?
The US system maintains separate dry volumes, including a dry pint and dry quart about 16% larger than their liquid counterparts. This engine handles liquid measures; dry goods are more reliably measured by weight in any case.
Should I measure baking ingredients by volume or weight?
Weight, wherever possible. A cup of flour can vary by 20% or more depending on how it is scooped and settled, whereas 120 grams is 120 grams. Volume measures are convenient for liquids but unreliable for flour, sugar and other compressible solids.
What is the difference between mL and cc?
Nothing — they are identical. One millilitre is exactly one cubic centimetre. Medical contexts often prefer cc while cooking and general use prefer mL.
How many teaspoons are in a tablespoon?
Three in both US and imperial usage. The US tablespoon is 14.78676478125 mL and the teaspoon exactly one third of that. Australian tablespoons are the exception at four teaspoons.
Is the litre an SI unit?
Not strictly. The SI unit of volume is the cubic metre; the litre is accepted for use with SI and defined as exactly one thousandth of a cubic metre. In practice it is used universally.
Is this volume converter free to use?
Yes. It is free, requires no account, and has no usage limits. ApexConverter is funded by contextual advertising, never by selling user data.
Is my data sent to a server?
No. The engine runs as Vanilla JavaScript inside your browser under our Zero-Server Client-Side Execution model. Your figures are computed locally and are never transmitted, logged, or stored.
How accurate is this calculator?
It applies the standard closed-form formula in IEEE-754 double precision, rounding only at the display layer. The engine is reconciled against an independent reference implementation before release.
Does it work on mobile?
Yes. The interface is mobile-first with numeric keypad hints and is tested down to a 320-pixel viewport with no horizontal scrolling.
Can I use it offline?
Largely, yes. Because computation is client-side, the page continues to calculate without a network connection once it has loaded.
Which currency does it use?
Amounts display in US$ accounting format, but the underlying mathematics is currency-agnostic. The result is identical in any currency, so simply read the figures in your own.
Why does a result show an em-dash?
An em-dash indicates the calculation is not defined for the inputs given — typically a division by zero or a value outside the valid domain. We show a dash rather than a misleading number.
How do I report an error?
Email apexconverter.praxiscalc@gmail.com with the tool URL, your exact inputs, the output received and the output you expected. Verified mathematical errors are patched within 72 hours.