O que é um/uma US Quart (qt)?
Formal Definition
The US liquid quart (symbol: qt) is a unit of volume in the US customary system equal to one quarter of a US gallon, or exactly 57.75 cubic inches. This equals approximately 946.352946 milliliters (0.946353 liters). The quart is divided into 2 US pints, 4 US cups, or 32 US fluid ounces.
The US liquid quart should be distinguished from the US dry quart (approximately 1,101.221 mL), which is used for measuring dry commodities, and from the imperial quart (approximately 1,136.523 mL), which is about 20% larger than the US quart. In everyday American usage, "quart" without qualification always means the US liquid quart.
Practical Scale
A quart is a familiar size in American daily life. A standard quart of milk, a quart container of soup, or a quart of motor oil are all common purchases. The quart represents a convenient intermediate volume — larger than a pint (16 fl oz) but smaller than a half-gallon (64 fl oz). Many food items in American grocery stores are sold in quart containers: ice cream, broth, juice, yogurt, and prepared soups.
Etymology
Latin Origins
The word "quart" derives from the Latin "quartus" (fourth), through the Old French "quarte." The name directly describes the unit's relationship to the gallon: a quart is one quarter (one fourth) of a gallon. This etymological transparency made the quart intuitive for medieval merchants — the word itself told you the relationship to the larger measure.
The Latin root "quartus" has given English numerous words: quarter, quartet, quarantine (originally 40 days — "quarantina" — but related to the concept of partitioning), and quart. In the measurement context, the quart has been used in English since at least the 14th century.
Precise Definition
Exact Definition
The US liquid quart is defined as exactly 1/4 of a US gallon = 57.75 cubic inches. Using the international inch (25.4 mm exactly): 1 US quart = 57.75 × (25.4 mm)³ = 57.75 × 16,387.064 mm³ = 946,352.946 mm³ = 946.352946 mL exactly.
Subdivisions
1 US quart = 2 US pints = 4 US cups = 8 US gills = 32 US fluid ounces. These relationships are all exact fractions of the gallon definition.
Comparison with Imperial Quart
The imperial quart (1,136.523 mL) is approximately 20% larger than the US quart (946.353 mL). This difference parallels the difference between the imperial and US gallons and affects all subdivisions: an imperial pint is larger than a US pint, an imperial cup is larger than a US cup, and so on.
História
Medieval English Origins
The quart evolved from medieval English liquid measures. As one quarter of a gallon, its history is inseparable from the gallon's history. When the English wine gallon was standardized at 231 cubic inches in 1706, the quart became 57.75 cubic inches. American colonists used this wine quart, and the United States retained it after independence.
Divergence from Britain
When Britain replaced all its gallons with the imperial gallon in 1824, the imperial quart became one quarter of the larger imperial gallon. The US continued using the wine quart. This created a persistent difference: US quart ≈ 946 mL vs. imperial quart ≈ 1,137 mL.
Modern American Usage
The quart became deeply embedded in American commerce during the 19th and 20th centuries. Milk was traditionally sold in quart glass bottles. Motor oil was sold in quart cans. Paint was available in quart tins. The quart container became a standard packaging size for many liquid and semi-liquid products in American grocery stores and hardware stores.
Uso atual
In American Commerce
The quart remains a standard packaging size in the US. Motor oil is sold in quart bottles (946 mL). Ice cream comes in quart containers. Soup, broth, and stock are sold in 32-oz (1 quart) cartons. Juice, half-and-half cream, and buttermilk are available in quart containers. Paint is sold in quarts, gallons, and 5-gallon buckets.
In the Kitchen
American recipes frequently specify ingredients in quarts. "One quart of chicken broth" and "two quarts of water" are typical recipe instructions. Stock pots and saucepans are often sized in quarts (2-quart, 4-quart, 8-quart). Slow cookers (crock pots) are rated by quart capacity (4-quart, 6-quart, 8-quart).
In Automotive
The quart is the standard unit for motor oil in the US. A typical oil change requires 4-6 quarts of oil. Transmission fluid, power steering fluid, and coolant are also measured in quarts. "Check the oil — you're a quart low" is a familiar phrase in American automotive culture.
Declining Outside the US
Outside the United States, the quart is rarely used. Canada replaced quarts with liters during metrication. The UK uses liters for commercial purposes. Most of the world has never used the quart, relying on liters and milliliters instead.
Everyday Use
Grocery Shopping
Americans encounter quarts regularly at the grocery store. A quart of milk (946 mL) is a standard size, smaller than a half-gallon but larger than a pint. A quart of yogurt or cottage cheese is a family-size container. A quart of fresh berries (using the dry quart, which is slightly larger) is a typical summer purchase.
Cooking and Kitchen
Home cooks think in quarts for larger liquid quantities. A pot of soup might need 2 quarts of broth. Making iced tea calls for 1-2 quarts of water. Cookware is sized in quarts: a 3-quart saucepan, a 6-quart Dutch oven, a 12-quart stock pot. Measuring cups typically show quart markings (4 cups = 1 quart).
Automotive Maintenance
The quart is the standard unit for automotive fluids. Motor oil bottles are labeled in quarts. Checking and adding oil is measured in quarts. "Your car needs 5 quarts of 5W-30" is a typical mechanic's instruction. Coolant is sold in quart and gallon containers.
In Science & Industry
Not Used in Science
The quart is not used in scientific contexts. American scientists use liters and milliliters exclusively. The quart appears in no scientific publications, laboratory protocols, or engineering specifications — even in the United States, scientific work uses metric units.
Historical Industrial Records
Historical American industrial records may reference quarts for production volumes, especially in the food and beverage industry. Dairy production was historically measured in quarts (and gallons) before metric reporting became standard.
Interesting Facts
The word 'quart' literally means 'a quarter' — from the Latin 'quartus' (fourth). A quart is exactly one quarter of a gallon, making the name perfectly descriptive.
A US quart (946 mL) is approximately 20% smaller than an imperial quart (1,137 mL). A British recipe calling for 'one quart' uses significantly more liquid than the same instruction in an American recipe.
The traditional American glass milk bottle held exactly one quart. Milkmen delivered quart bottles to doorsteps across America from the early 1900s until the practice largely ended in the 1970s-1980s.
A quart of water weighs approximately 2.09 pounds (946 grams). A quart of motor oil weighs about 1.88 pounds (roughly 850 grams) because oil is less dense than water.
In the US automotive industry, engines are described by their oil capacity in quarts. A typical 4-cylinder engine holds 4-5 quarts, a V6 holds 5-6 quarts, and a V8 holds 6-8 quarts.
The US dry quart (1,101 mL) is about 16% larger than the US liquid quart (946 mL). The dry quart is defined as 1/32 of a US dry bushel and is used for measuring berries, nuts, and other dry goods.
A human stomach can hold approximately 1 quart (about 1 liter) of food and liquid when full, though comfortable capacity is less.
Standard American 'quart-size' freezer bags have become ubiquitous in TSA airport security — the 'quart bag' rule allows passengers to carry liquids in containers of 3.4 oz (100 mL) or less in a single quart-size bag.
Regional Variations
United States
The quart is used daily in the United States for cooking, shopping, and automotive maintenance. It is a standard packaging size for many liquid products.
Canada
Canada formerly used both the US quart (in some trade with the US) and the imperial quart. Since metrication, Canada uses liters exclusively, though older Canadians may still reference quarts.
United Kingdom
The imperial quart (1,137 mL) was used in the UK until metrication. Today, the quart is not used commercially in the UK, though it appears in older recipe books and historical references.
Rest of the World
The quart is not used outside English-speaking countries and their former colonies. The liter serves the same function globally.