Article — Quarts to Gallons Converter
Quarts to gallons: the exact 4:1 ratio, in both US and UK systems
- The quarts to gallons formula
- Quarts to gallons for motor oil
- Quarts to gallons in the paint aisle
- Quarts in cooking and canning
- US versus UK gallon: same 4 quarts, different sizes
- Water capacity: jugs, coolers, and pools in quarts
- Common quarts to gallons mistakes
- Why a quart is one quarter of a gallon
1 gallon = 4 quarts, exactly. Divide quarts by 4 to get gallons, multiply gallons by 4 to reverse. The 4:1 ratio is the same in the US customary and imperial UK systems — the absolute sizes differ by about 20% (1 US gal = 3.785 L vs 1 imp gal = 4.546 L), but four quarts always make a gallon in either system. The word "quart" comes from Latin quartus, "the fourth." It is the only common conversion in volume measurement where the answer is built into the etymology.
This calculator handles the conversion both directions with no rounding error. Useful when you are buying motor oil by the quart but the manual specifies gallons, scaling a 5-gallon paint job down to a single quart sample, or sizing a canning batch.
The quarts to gallons formula
gal = qt / 4. That is the full conversion. 8 qt = 2 gal, 12 qt = 3 gal, 22 qt = 5.5 gal. Halving twice (qt → halve → halve = gal) is faster than dividing by 4 in your head.
2 qt = 0.5 gal half gallon4 qt = 1 gal standard milk jug5 qt = 1.25 gal typical oil change8 qt = 2 gal 2-gal jug16 qt = 4 gal large canning pot20 qt = 5 gal 5-gal bucketThe 4 is exact — it is part of the definitions of the two units, not a measured conversion factor. There is no rounding involved. The only error in any quarts-to-gallons conversion is the precision setting you choose for the display.
Quarts to gallons for motor oil
US motor oil is sold by the quart, but service intervals and reservoir capacities are usually published in gallons. A typical passenger-car oil change takes 4 to 6 quarts — between 1 and 1.5 gallons. The mismatch causes more parts-counter confusion than any other automotive volume figure.
- 4-cylinder engine = 4 to 5 qt (1.0 to 1.25 gal)
- V6 engine = 5 to 6 qt (1.25 to 1.5 gal)
- V8 engine = 6 to 8 qt (1.5 to 2.0 gal)
- Heavy-duty diesel = 12 to 15 qt (3.0 to 3.75 gal)
- Class 8 truck (Cummins, Detroit) = 28 to 44 qt (7 to 11 gal)
- Motorcycle (typical) = 2 to 4 qt (0.5 to 1.0 gal)
The most common cars need 5 qt for a full oil change. Buying a 1-gallon jug from a parts store gives you 4 qt, leaving you a quart short. Either buy an extra quart, or buy a 5-quart jug — which is the size most auto-parts stores actually stock for this reason. Overfilling by a quart is just as bad as underfilling.
Quarts to gallons in the paint aisle
Paint comes in three standard sizes: 1 quart (sample), 1 gallon (single room), and 5 gallons (whole house). The pricing usually rewards bigger cans — a 5-gallon bucket per quart costs roughly 40% less than buying quart cans one at a time.
Coverage math is easier in gallons. One US gallon of latex paint covers about 350 square feet with one coat. Convert quarts to gallons first, then multiply by 350. A 6-quart job covers 6/4 × 350 = 525 sq ft. The arithmetic is harder if you leave the figure in quarts.
Buying paint, always round up after the quarts-to-gallons conversion. A 7-quart job (1.75 gal) calls for 2 gallons, not 1.75. Mid-job touch-ups need leftover paint, and the colour-match service at the store may not exactly reproduce a custom mix months later.
Quarts in cooking and canning
Stockpots and slow cookers are sold in quarts (a 6-qt Instant Pot is the best-selling size). Canning recipes specify quart jars. But food-service recipes for restaurants and caterers usually scale to gallons. Converting between the two is constant kitchen work.
Home brewers buy 10-gallon (40-quart) kettles to brew 5-gallon batches, leaving headroom for boil-off and foam. The 40-quart figure is the kettle volume; the 5-gallon figure is the finished beer. Two different quart counts in one workflow.
US versus UK gallon: same 4 quarts, different sizes
Both the US and the UK measure liquids in gallons divided into 4 quarts. The internal ratio is identical. What differs is the absolute volume of every unit.
- 1 US gallon = 3.785 L = 128 US fl oz (Queen Anne wine gallon, 231 in³)
- 1 imperial gallon = 4.546 L = 160 imperial fl oz (1824 UK Weights and Measures Act)
- Imperial gallon ÷ US gallon = 1.201 (imperial is 20.1% bigger)
- 1 US quart = 946 mL — about 5% less than a litre
- 1 imp quart = 1136 mL — about 14% more than a litre
- 1 imperial quart in US quarts = 1.201 US qt
Before 1824, the UK used three different gallons at the same time: a wine gallon (231 in³) for spirits, an ale gallon (282 in³) for beer, and a corn gallon (268.8 in³) for grain. The 1824 Weights and Measures Act unified them into one Imperial gallon of 277.42 in³. The US — already independent — kept the wine gallon, which is why the modern US gallon is about 20% smaller than the imperial gallon.
Water capacity: jugs, coolers, and pools in quarts
Drinking-water containers and household tanks are usually labelled in gallons, but the smaller subdivisions matter for daily use. A 5-gallon water cooler holds 20 quarts — about 76 litres. A standard bathtub holds 35-50 gallons (140-200 quarts), and a household water heater is typically 40-50 gallons.
1-gal jug = 4 qt = 3.78 L5-gal cooler = 20 qt = 18.9 L40-gal heater = 160 qt = 151 L200-gal aquarium = 800 qt = 757 L20,000-gal pool = 80,000 qt = 75,700 LCommon quarts to gallons mistakes
The 4:1 ratio is simple, but the surrounding context is where errors creep in.
A US liquid quart is 946 mL. A US dry quart is 1101 mL — about 16% larger. Dry quarts are used in the US for berries, mushrooms, and produce sold by volume. A "quart of strawberries" at a farmstand is a dry quart, not 946 mL. The dry-quart/dry-gallon ratio is still 4:1, but the absolute amount is different from the liquid system.
1 US quart = 0.946 L. The 5.4% gap matters for any technical or medical measurement: 1 L of saline is not 1 US quart. UK quart is the opposite — 13.7% larger than a litre. Treat them as different units and convert each time.
Why a quart is one quarter of a gallon
Both terms entered English from medieval Latin. Gallon traces back through Old French galon (a measure for wine) to Late Latin galleta. Quart comes directly from Latin quartus, "the fourth." The word literally tells you the ratio.
Halves of a gallon were called pottles, the eighths were pints, and the sixteenths were cups — an old English binary ladder that survived into modern American kitchens. Counting backward from 128 fl oz per US gallon, every smaller unit appears by halving. The quart sits at the second step down.