Why this matters
Volume conversion seems trivial until you discover that a US gallon and a UK gallon differ by nearly 20 percent. A recipe calling for one cup of flour produces different results depending on whether you measure with a US legal cup (240 ml), a metric cup (250 ml), or a US cooking cup (236.6 ml). These are not rounding errors — they are fundamentally different definitions that have existed for centuries and continue to cause problems in international cooking, pharmaceutical dosing, and industrial manufacturing.
The practical impact is significant. A British recipe that calls for a pint of milk means 568 ml, while the same instruction in an American cookbook means 473 ml. A pharmaceutical formulation specified in fluid ounces will deliver a different dose depending on whether the measuring country uses the US or imperial standard. Using an approximate conversion factor introduces compounding errors when you chain multiple conversions together. This converter uses exact statutory conversion factors — 1 US gallon equals exactly 3.785411784 liters, 1 UK gallon equals exactly 4.54609 liters — so there is no rounding loss in the computation.
The tool covers 11 units spanning three measurement systems: metric (milliliter, liter, cubic meter), US customary (teaspoon, tablespoon, fluid ounce, cup, pint, quart, gallon), and UK imperial (gallon). Enter a value in any unit and every equivalent is displayed simultaneously with individual copy buttons, making it straightforward to pull the exact number you need for your context.
Reference table
| Unit | Exact definition | Approximate ml |
|---|---|---|
| US teaspoon | 1/6 US fl oz | 4.93 ml |
| US tablespoon | 3 US teaspoons | 14.79 ml |
| US fluid ounce | 1/128 US gallon | 29.57 ml |
| US cup | 8 US fl oz | 236.59 ml |
| US gallon | 231 cubic inches | 3785.41 ml |
| UK gallon | 4.54609 liters | 4546.09 ml |
How to use it
Enter a volume value in the input field.
Select the source unit from the dropdown covering all 11 supported units.
View all equivalent values displayed simultaneously across metric, US, and UK systems.
Click the copy button next to any result to grab that specific conversion.
Testing your result
Verify a conversion by checking it against a known exact relationship. For example, 1 US gallon should convert to exactly 3.785411784 liters and 128 US fluid ounces. Test a round-trip: convert 1 liter to US gallons, then convert that result back to liters — you should get exactly 1.000 (not 0.999 or 1.001). For cooking conversions, compare the tablespoon-to-ml result against your measuring cup: 1 US tablespoon should show 14.787 ml. If you regularly cook with Australian recipes, confirm that their tablespoon (20 ml) is not the same as the US tablespoon the tool uses.
Cross-reference your results with an authoritative source like the NIST (National Institute of Standards and Technology) conversion tables. Pay particular attention to the cup and gallon values since those are the units most likely to vary by country. If you are converting a recipe with multiple volume ingredients, convert each one individually rather than converting the total — this avoids rounding accumulation that could throw off the final dish. For scientific or pharmaceutical work, always use the milliliter or liter column since metric units are unambiguous across all contexts.
Common mistakes
Assuming all gallons, cups, and fluid ounces are the same — the US and UK systems diverge significantly.
Using the US cup (236.6 ml) when a recipe from Australia or New Zealand expects the metric cup (250 ml).
Rounding intermediate conversions when chaining them, which introduces compounding error.
Edge cases and options
The teaspoon-to-tablespoon ratio is always 3:1 within the same system, but the tablespoon itself varies: US (14.79 ml), Australian (20 ml), and metric (15 ml). This tool uses US customary definitions throughout. For very small volumes like a single milliliter, the conversion to cubic meters produces a very small decimal (0.000001) that is still exact. The cubic meter option is useful for engineering contexts where large fluid volumes are specified in SI base units. All conversions are computed from the exact statutory factors, so no precision is lost regardless of which unit you start from.
Real-world use cases
A home cook converting a British baking recipe to US measurements for a kitchen stocked with American measuring tools.
A chemistry student converting between milliliters and fluid ounces to prepare a lab solution from a protocol published in the US.
A fuel purchaser comparing prices per US gallon versus per liter at an international border station.
Frequently asked questions
Q: What's the difference between US and UK gallons?
A: US gallon equals 3.785 L (231 cubic inches). UK (imperial) gallon equals 4.546 L. UK gallons are roughly 20% larger. Always specify which you mean.
Q: How many teaspoons in a tablespoon?
A: 3 teaspoons (US) equals 1 tablespoon equals 14.79 ml. Australian tablespoons are 20 ml (4 teaspoons). Pick the one matching your recipe's origin.
Q: Is 1 cup 240 ml or 250 ml?
A: US legal cup equals 240 ml. Metric cup (Australia, NZ, Canada) equals 250 ml. US cooking cup equals 236.6 ml. For precision, use ml.
Q: Are conversions exact?
A: Yes — 1 US fl oz equals 29.5735295625 ml exactly, 1 US gal equals 3.785411784 L exactly, 1 UK gal equals 4.54609 L exactly.
Q: Why does the cup value look wrong for my recipe?
A: Check the recipe's country of origin. US, metric, and Australian cups all differ slightly. Convert to milliliters for an unambiguous reference.
Start using it now
Try the Volume Converter tool. See also Cooking Converter, Weight Converter, and Weight Converter.
