Converting volume: liters, gallons, cups and ml without guessing
Every common volume unit — milliliters, US cups, US gallons, quarts, pints — is a fixed multiple of one liter. Once that multiple is known, converting any amount between any two of them is one multiplication (to go from liters to the target unit) or one division (to go back to liters).
The method
converted amount = amount in liters ÷ (liters per target unit), or equivalently multiply by (target units per liter). The constants worth knowing: 1 US gallon = 3.785411784 L, 1 US cup = 0.236588236 L (about 236.6 ml), 1 US quart = 0.946352946 L.
A real example: 5 US gallons of paint, in liters
5 × 3.785411784 = 18.92705892, so 5 gallons is about 18.93 liters.
A real example: 2.5 cups of liquid, in milliliters
First find liters: 2.5 × 0.236588236 = 0.59147059 L. Then convert to milliliters by multiplying by 1,000: 0.59147059 × 1000 = 591.47059, so 2.5 US cups is about 591.5 ml — useful when a recipe is written in cups but a kitchen scale or jug only reads in ml.
A real example: converting back from milliliters to cups
A jug reads 500 ml and the recipe wants cups. Convert to liters first (500 ÷ 1000 = 0.5 L), then divide by the liters-per-cup constant: 0.5 ÷ 0.236588236 = 2.1134, so 500 ml is about 2.11 US cups. Going from a small unit to a big one is always a division once everything is routed through liters.
US gallons are not imperial gallons
A US liquid gallon (3.785411784 L) and an imperial gallon (4.54609 L) differ by about 20% — using the wrong one on a recipe, fuel figure or tank capacity from a UK source silently produces a volume that's off by a fifth. Always confirm which gallon a source means before converting, especially on anything imported or converted from a UK unit.
What volume conversion doesn't account for
Converting units doesn't account for density — a cup of flour and a cup of water are the same volume but very different weights, so a recipe that actually needs weight (common in baking) isn't solved by a volume conversion alone. For that, a kitchen scale and the ingredient's density are what matter, not another decimal place on the conversion.
Run your own numbers
The free Volume Converter converts between liters, milliliters, US gallons, quarts, pints, cups, fluid ounces and cubic meters instantly, entirely on your device.