UK to US Units Converter

The UK to US units converter bridges the gap between British imperial and American customary measurement systems. Despite sharing common names like gallons, pints, tons, and fluid ounces, UK and US units often represent different quantities — sometimes dramatically so. A UK gallon of petrol is nearly 20% larger than a US gallon, while a UK fluid ounce is slightly smaller than its American counterpart. These discrepancies can cause major errors in recipes, fuel calculations, shipping weights, and international trade if not converted correctly.

This converter handles four key categories of measurement where UK and US standards diverge: volume (gallons, quarts, pints, fluid ounces, cups, tablespoons, teaspoons), weight (long tons vs. short tons, hundredweight, and the uniquely British stone unit), length (imperial vs. US survey feet), and paper sizes (A-series vs. US letter/tabloid). Each conversion uses the exact, internationally agreed-upon factors to ensure precise results every time.

Each category uses a specific set of conversion factors derived from the legal definitions of these units. The most significant difference is in volume, where the UK gallon is defined by the imperial standard while the US gallon follows the older wine gallon standard.

For volume units, note the interesting reversal: the UK gallon is larger than the US gallon, but the UK fluid ounce is smaller. This means that quick "multiply by 1.2" mental math works for gallons, quarts, and pints but fails for fluid ounces, where you must multiply by approximately 0.961 instead.

The split between UK and US volume measurements dates back to 1824, when Britain adopted the imperial system of weights and measures and redefined the gallon as the volume of 10 pounds of distilled water at 62°F — equivalent to 4.54609 liters. The United States, having already established its own customary system based on the older Queen Anne wine gallon of 1707, kept its definition: 231 cubic inches, or 3.78541 liters. The result is that an imperial gallon is roughly 1.2 US gallons, a difference that persists to this day.

This difference cascades through all derived volume units. A UK pint (1/8 of a UK gallon) is 20 UK fluid ounces of approximately 28.4 mL each, while a US pint (1/8 of a US gallon) contains 16 US fluid ounces of approximately 29.6 mL each. So a UK pint has more ounces but each is slightly smaller — the net effect is that a UK pint is about 568 mL, versus 473 mL for a US pint. This is why a British pub pint feels noticeably larger than an American one.

Cooking and baking are the domains most affected by these volume differences. A British recipe calling for a "cup" of flour yields 20% more flour than the same instruction in an American recipe, which can ruin baked goods that depend on precise ratios. The tablespoon and teaspoon differences — though smaller in absolute terms — can similarly throw off seasoning and leavening agents in recipes that depend on chemical precision.

The converter is organized by measurement category to help you find the right conversion quickly:

1. Choose a category: Select from Volume, Weight, Length, or Paper using the tab buttons at the top. The conversion options underneath update automatically.
2. Pick a conversion type: Use the dropdown to select which specific UK unit you want to convert — for example, "UK Gallons to US Gallons" or "Stone to Pounds."
3. Enter the value: Type in or use the arrows to set the quantity you want to convert. The result displays instantly in the highlighted card.
4. Check the quick reference: At the bottom of the page, common conversions are pre-calculated for easy lookup without typing.

The Key Differences section explains why each conversion is necessary and where the units are primarily used, helping you understand the context — not just the numbers.

Weight measurement is another area of significant divergence. The UK uses the long ton of 2,240 pounds (or 20 hundredweight of 112 pounds each), while the US uses the short ton of 2,000 pounds (20 hundredweight of 100 pounds each). A UK hundredweight at 112 pounds is 12% heavier than a US hundredweight at 100 pounds — a critical distinction in commodities trading, shipping freight calculations, and industrial supply chains.

The stone is uniquely British. Equal to 14 pounds, the stone is the standard unit for expressing human body weight in the UK and Ireland. A person weighing 11 stone is roughly 154 pounds. While Americans always report weight in pounds, Britons routinely use the stone-pound combination (e.g., "11 stone 4 pounds"). This converter translates directly between stones and pounds, making it effortless to understand British health data, weight loss goals, or sports statistics that use stones.

The metric ton (tonne = 1,000 kg = 2,204.6 lb) is now the international standard for industrial and scientific weight, but the UK and US ton variants persist in specific industries. UK road freight limits are sometimes quoted in long tons, while US trucking regulations use short tons. The IMO (International Maritime Organization) uses metric tonnes for shipping, but regional practices often default to the traditional national ton.