How many ml in a cup?

US cup = 236.588 mL. Metric cup = 250 mL. UK cup = 284.131 mL. Varies by country.

How many tablespoons in a cup?

US: 16 tablespoons = 1 cup (236.588 mL). Metric: 250 mL ÷ 15 mL = 16.67 tbsp.

What is the difference between US and UK gallon?

UK gallon (4.546 L) is 20% larger than US gallon (3.785 L). A car rated 40 UK mpg = ~33.3 US mpg.

What is a US dry gallon?

US dry gallon = 4,404.88 mL — 16.3% larger than liquid gallon (3,785.41 mL). Used historically for dry goods; now largely obsolete.

🧪 Volume Conversion Calculator

Convert between liters, milliliters, US & UK gallons, cups, fl oz, tablespoons, cubic meters, cubic feet, barrels, acre-feet and 70+ volume units — with SI cubic volume formulas, US vs UK gallon history, cooking measures & industrial volume formulas in MathJax

70+ Units SI · US Customary · UK Imperial · Cooking · Industrial L ↔ gal · ml · cups · ft³ · m³ Free & Instant

🔄 Volume Unit Converter

Enter Value From Unit

Result To Unit

1 gal (US) = 3.785 L

Formula: value × 3.785412

🌍 All Units at Once

💡 Key fact: \(1\,\text{L} = 1\,\text{dm}^3 = 10^{-3}\,\text{m}^3 = 1000\,\text{cm}^3 = 1000\,\text{mL}\). US gallon = 231 in³ = 3.785411784 L (exact by US law). UK imperial gallon = 4.54609 L (exact, defined 1985). All conversions in this calculator use mL as the base unit with exact factors.

📖 How to Use This Volume Conversion Calculator

1

Filter by Unit Category (Optional)
Choose Metric/SI (L, mL, cL, dL, hL, kL, µL), US Customary (gal, qt, pt, cup, fl oz, bushel, peck, dry gallon), UK Imperial (gal UK, qt UK, pt UK, fl oz UK, gill), Cooking (cups, tbsp, tsp — US/metric/UK variants, drop, pinch), Cubic (m³, cm³, mm³, ft³, in³, yd³, km³), or Industrial (acre-foot, barrel, cord, board foot).
2

Enter Your Volume Value
Type the numeric value in "Enter Value." Works across the full range — from a microlitre (0.001 mL) in a laboratory syringe to cubic kilometres (10¹² L) for ocean volumes.
3

Select From and To Units
Choose source and target units. The result and exact multiplication factor appear instantly in the blue result box.
4

Use Quick-Convert Buttons
Click preset conversions — gal (US)↔L, L↔mL, m³→L, cup→mL, ft³→L, gal UK→L — to instantly set both dropdowns for the most frequently needed conversions.
5

View All Units at Once & Copy
The "All Units at Once" panel displays your volume in every supported unit simultaneously. Click "📋 Copy Result" for use in recipes, engineering specs, tank calculations, or regulatory filings.

📐 Volume Unit Conversion Reference Table

From	To	Multiply By	Mathematical Expression
1 US gallon	liters	3.785412	\( 1\,\text{gal (US)} = 231\,\text{in}^3 = 3.785411784\,\text{L} \) (exact)
1 UK gallon	liters	4.54609	\( 1\,\text{gal (UK)} = 4.54609\,\text{L} \) (exact, 1985)
1 liter	US gallons	0.264172	\( 1\,\text{L} = 1/3.785412\,\text{gal (US)} \)
1 cubic meter	liters	1,000	\( 1\,\text{m}^3 = 10^3\,\text{L} = 10^6\,\text{mL} \)
1 cubic foot	liters	28.31685	\( 1\,\text{ft}^3 = (0.3048)^3\,\text{m}^3 = 28.3168\,\text{L} \)
1 cubic inch	mL	16.38706	\( 1\,\text{in}^3 = (0.0254)^3\,\text{m}^3 = 16.3871\,\text{mL} \)
1 US cup	mL	236.5882	\( 1\,\text{cup (US)} = \tfrac{1}{16}\,\text{gal} = 236.588\,\text{mL} \)
1 US fl oz	mL	29.57353	\( 1\,\text{fl oz (US)} = \tfrac{1}{128}\,\text{gal} = 29.5735\,\text{mL} \)
1 petroleum barrel	liters	158.9873	\( 1\,\text{bbl} = 42\,\text{gal (US)} = 158.987\,\text{L} \)
1 acre-foot	cubic meters	1,233.48	\( 1\,\text{ac·ft} = 43{,}560\,\text{ft}^2 \times 1\,\text{ft} = 1{,}233.48\,\text{m}^3 \)

🌊 Understanding Volume — A Complete Science & Engineering Guide

Volume is the three-dimensional extent of space enclosed by a surface — the amount of three-dimensional space a substance occupies. It is one of the most universally needed measurements in everyday life, engineering, science, and commerce: from measuring cooking ingredients in tablespoons and cups, to specifying tank capacities in gallons, to calculating concrete for a foundation in cubic metres, to measuring global ocean flows in cubic kilometres per year.

Volume unit conversion is notoriously confusing because multiple competing systems exist simultaneously. The metric (SI) system uses litres and cubic metres; the US Customary system uses fluid ounces, cups, pints, quarts, and gallons; the UK Imperial system uses its own fluid ounces, pints, and gallons — all different sizes to their US counterparts. And then there are specialist systems: cooking measures, petroleum industry barrels, lumber board-feet, water management acre-feet, and astronomical units. This calculator handles all of them with precision.

SI Volume — Definitions & Exact Relationships

\( 1\,\text{m}^3 = 10^3\,\text{dm}^3 = 10^6\,\text{cm}^3 = 10^9\,\text{mm}^3 \quad \text{(exact, SI)} \)

\( 1\,\text{L} = 1\,\text{dm}^3 = 10^{-3}\,\text{m}^3 = 10^3\,\text{mL} = 10^3\,\text{cm}^3 \quad \text{(litre definition)} \)

\( V_{\text{cube}} = a^3 \qquad V_{\text{sphere}} = \tfrac{4}{3}\pi r^3 \qquad V_{\text{cylinder}} = \pi r^2 h \qquad V_{\text{cone}} = \tfrac{1}{3}\pi r^2 h \)

\( V_{\text{cuboid}} = l \times w \times h \qquad V_{\text{prism}} = A_{\text{base}} \times h \qquad V_{\text{pyramid}} = \tfrac{1}{3} A_{\text{base}} \times h \)

\(a\) = edge length · \(r\) = radius · \(h\) = height · \(l, w\) = length, width · \(A_{\text{base}}\) = base area · 1 L of water at 4°C has mass exactly 1 kg (basis of original litre definition, 1793 France) · SI Volume SI unit: m³; accepted unit: litre (L)

🇺🇸🇬🇧 US Gallon vs UK Imperial Gallon — History & Exact Definitions

The single most confusing aspect of volume conversion for most users is the US vs UK gallon difference. They share the same name but differ by approximately 20% in volume. Understanding why requires a brief excursion into measurement history — and knowing the exact legal definitions that govern modern engineering specifications.

US Gallon vs UK Imperial Gallon — Exact Definitions

\( 1\,\text{gal (US)} = 231\,\text{in}^3 \quad \text{(exact, US law)} = (231 \times 16.387064\,\text{mL}) = 3{,}785.411784\,\text{mL (exact)} \)

\( 1\,\text{gal (UK)} = 4{,}546.09\,\text{mL (exact, UK Weights and Measures Act 1985)} \)

\( \frac{\text{gal (UK)}}{\text{gal (US)}} = \frac{4546.09}{3785.41} = 1.20095... \approx 20\%\text{ larger} \)

\( \text{US: } 1\,\text{gal} = 4\,\text{qt} = 8\,\text{pt} = 16\,\text{cups} = 128\,\text{fl oz} \quad \text{(US fl oz = }29.5735\text{ mL)} \)

\( \text{UK: } 1\,\text{gal} = 4\,\text{qt} = 8\,\text{pt} = 160\,\text{fl oz} \quad \text{(UK fl oz = }28.4131\text{ mL)} \)

History: US gallon = Queen Anne's wine gallon (1706). UK imperial gallon defined 1824 as volume of 10 lbs of water at 62°F, later metricated to 4.54609 L (1985 exact). The 231 in³ definition for the US gallon is itself derived from the 1959 international inch (25.4 mm exactly).

📌 Worked Example — Fuel Economy: UK mpg vs US mpg

Problem: A car achieves 40 miles per UK gallon. What is this in US mpg and in L/100km (European standard)?

UK mpg → US mpg: \( 40\,\text{mpg (UK)} \times \frac{3.785412}{4.546090} = 40 \times 0.83267 = \mathbf{33.31\,\text{mpg (US)}} \)

L/100km: \( \frac{235.215}{33.31\,\text{mpg (US)}} = \mathbf{7.06\,\text{L/100km}} \)

Note: In the UK, fuel economy used to be stated in mpg (imperial), but EU regulations required L/100km labelling since 2011. This US/UK mpg confusion regularly affects car comparisons — a UK car rated at 40 mpg is NOT the same as a US car rated at 40 mpg; the UK figure sounds better but only because the imperial gallon is larger.

🍳 Cooking Volume Units — US, Metric & International Kitchen Measures

Precise volume measurement is essential in cooking and baking — especially when scaling recipes up or down, adapting recipes from one country's standards to another, or converting between wet and dry measurements. The cup, tablespoon, and teaspoon are the backbone of recipe volume in English-speaking countries, but their exact sizes differ between the US, UK, Australia, Canada, and metric systems.

Cooking Volume Relationships

\( \text{US: } 1\,\text{cup} = 16\,\text{tbsp} = 48\,\text{tsp} = 8\,\text{fl oz} = 236.588\,\text{mL} \)

\( \text{Metric: } 1\,\text{cup} = 250\,\text{mL} = 16.\overline{6}\,\text{tbsp (metric)} \quad \text{(tbsp metric = 15 mL)} \)

\( \text{Australian: } 1\,\text{cup} = 250\,\text{mL} \quad 1\,\text{tbsp (AU)} = 20\,\text{mL} \quad 1\,\text{tsp} = 5\,\text{mL} \)

\( \text{UK: } 1\,\text{tbsp (UK)} = 17.758\,\text{mL} \qquad 1\,\text{tsp (UK)} = 5.919\,\text{mL} \)

\( \text{US tsp} = 4.929\,\text{mL} \qquad \text{US tbsp} = 14.787\,\text{mL} \qquad \text{drop (medical)} = 0.05\,\text{mL} \)

Recipe conversions: US cup → mL: ×236.6 · Metric cup → US cup: ×1.0567 · AU tbsp → US tbsp: 20/14.787 = 1.352 (AU tablespoon is 35% larger than US) · Pinch ≈ 0.31 mL ≈ 1/16 tsp · Dash ≈ 0.62 mL ≈ 1/8 tsp (US bar measure)

🍳 Baking precision tip: For dry ingredients, volume measures (cups, tbsp) are notoriously imprecise because packing affects density. 1 cup of sifted flour ≈ 100–115 g; 1 cup of packed flour ≈ 130–145 g — a ~35% difference that can ruin a recipe. Professional bakers always weigh dry ingredients in grams. For liquids, \(V\,[\text{mL}] = m\,[\text{g}] / \rho\,[\text{g/mL}]\). Water: 1 mL = 1 g. Milk: 1 mL ≈ 1.03 g. Oil: 1 mL ≈ 0.92 g.

📌 Worked Example — Scaling a Recipe (US cups to metric mL)

Problem: A US recipe requires 2½ cups flour, ¾ cup milk, and 3 tablespoons butter. Convert to millilitres for a metric kitchen.

Flour: \( 2.5 \times 236.588 = \mathbf{591.5\,\text{mL}} \approx 592\,\text{mL} \)

Milk: \( 0.75 \times 236.588 = \mathbf{177.4\,\text{mL}} \approx 177\,\text{mL} \)

Butter: \( 3 \times 14.787 = \mathbf{44.4\,\text{mL}} \approx 44\,\text{mL} \) (or 42.5 g if density ≈ 0.958 g/mL)

Practical note: Nearest metric measuring cup marks: 600 mL flour, 175 mL milk, 45 mL butter — near-enough accurate for baking.

📐 Cubic Volume Units — Engineering & Construction

Cubic Volume — Exact Relationships

\( 1\,\text{ft}^3 = (12\,\text{in})^3 = 1728\,\text{in}^3 = (0.3048\,\text{m})^3 = 0.0283168\,\text{m}^3 = 28.3168\,\text{L} \)

\( 1\,\text{yd}^3 = (3\,\text{ft})^3 = 27\,\text{ft}^3 = 0.764555\,\text{m}^3 = 764.555\,\text{L} \)

\( 1\,\text{in}^3 = (0.0254)^3\,\text{m}^3 = 1.6387064 \times 10^{-5}\,\text{m}^3 = 16.3871\,\text{mL (exact)} \)

\( 1\,\text{m}^3 = 35.3147\,\text{ft}^3 = 1.30795\,\text{yd}^3 = 264.172\,\text{gal (US)} \)

\( 1\,\text{km}^3 = 10^9\,\text{m}^3 = 10^{12}\,\text{L} \approx 0.2399\,\text{mi}^3 \)

All cubic Imperial factors exact from 1959 international inch: 1 in = 25.4 mm exactly · 1 in³ = 16.387064 mL exactly · 1 ft³ = 28,316.846592 mL exactly · Common construction uses: concrete poured and priced in cubic yards (yd³); timber shipped in cubic metres (m³); HVAC duct design in cubic feet (ft³)

🏭 Industrial Volume Units — Oil, Water & Lumber

🛢️

Petroleum Barrel (bbl)

1 bbl = 42 US gallons = 158.987 L (exact). The standard unit for crude oil trading worldwide. Defined 1872 by Pennsylvania oil producers. 1 metric tonne of crude ≈ 7.3–7.5 bbl (depends on API gravity). Global daily oil production: ~100 million bbl/day ≈ 15.9 billion L/day.

💧

Acre-Foot (ac·ft)

1 ac·ft = 1,233.48 m³ = 325,851 US gallons. Volume of water covering 1 acre (4,047 m²) to a depth of 1 foot. Used for US reservoir storage, irrigation rights, and groundwater management. Lake Mead capacity: ~36.7 km³ ≈ 29.75 million ac·ft.

🪵

Cord & Board-Foot

1 cord = 128 ft³ = 3.625 m³. Standard firewood measure: stack 4 ft × 4 ft × 8 ft. 1 board-foot = 144 in³ = 2.3597 L. Lumber unit = 1 ft × 1 ft × 1 in thick. A typical house frame uses ~10,000 board-feet of lumber.

🥃

Hogshead & Drum

US hogshead: 63 gal = 238.48 L. Used for bourbon whiskey production (Kentucky law: barrel ≤ 53 gal). US petroleum drum: 55 gal = 208.2 L. Standard industrial drums used in chemical and oil industries globally.

🌊 Volume Reference Table — Water, Oceans & Atmosphere

Object / System	Volume (m³)	Volume (L)	Notes
🥄 Teaspoon (metric)	5×10⁻⁶	0.005	5 mL exactly
🥛 Cup (metric)	2.5×10⁻⁴	0.25	250 mL exactly
🍾 Wine bottle (standard)	7.5×10⁻⁴	0.75	750 mL — Bordeaux standard since 1970s
⛽ US gallon (fuel)	3.785×10⁻³	3.785	231 in³ = 3.785412 L (exact)
🛁 Standard bathtub	~0.25	~250	Typical fill ~120–150 L
🛢️ Petroleum drum (55 gal)	0.2082	208.2	Also 200 L metric drum
🛢️ Oil barrel (bbl)	0.15899	158.99	42 US gal — global crude oil standard
🏊 Olympic swimming pool	2,500	2.5×10⁶	50 m × 25 m × 2 m
🏞️ Lake Geneva	8.9×10¹⁰	8.9×10¹³	720 km² × 154.4 m avg depth
🌊 World Ocean total	1.335×10¹⁸	1.335×10²¹	~97.5% of Earth's liquid water

Written & Reviewed by Num8ers Editorial Team — Metrology, Chemical Engineering, Food Science & Water Resources Management Specialists Last updated: April 2026 · Conversion factors verified against NIST SP 811 (2008), US Code 15 U.S.C. § 205 (metric conversion law), UK Weights and Measures Act 1985, ISO 80000-3 (Space and Time), BIPM SI Brochure 9th edition (2019). US gallon: 231 in³ exact; 1 in = 25.4 mm exact → 1 gal (US) = 3.785411784 L exact. UK gallon: 4.54609 L exact (SI 1985).

❓ Frequently Asked Questions — Volume Conversion

How many liters in a US gallon?

1 US gallon = 3.785411784 L (exact). Defined as 231 cubic inches (231 in³) under US law. Reverse: 1 L = 0.264172 US gallons. The US gallon originates from the Queen Anne wine gallon of 1706. It is approximately 20% smaller than the UK (imperial) gallon of 4.546 L.

How many liters in a UK (imperial) gallon?

1 UK gallon = 4.54609 L (exact, UK Weights and Measures Act 1985). Reverse: 1 L = 0.21997 UK gallons. The imperial gallon was defined in 1824 as the volume of 10 pounds of distilled water at 62°F and 30 inches of mercury pressure. It is about 20% larger than the US gallon. UK petrol is sold in litres today, but UK miles-per-gallon figures still use imperial gallons.

How many milliliters in a cup?

It depends on which cup: US cup = 236.588 mL (exactly 1/16 US gallon). Metric cup = 250 mL (used in Australia, Canada, New Zealand, and international nutrition). UK cup = 284.131 mL (½ UK pint — rarely used in modern recipes). Most online recipes use the US cup unless they specify "metric." When in doubt, use a measuring jug in mL.

How many ml in a tablespoon?

US tablespoon = 14.787 mL (exactly ½ US fl oz = 1/16 US cup). Metric tablespoon = 15 mL (used in Canada, international nutrition, and UK since 1970s). Australian tablespoon = 20 mL (significantly larger — often causes recipe confusion). UK traditional = 17.758 mL (½ UK fl oz). Always verify recipe source country when tbsp measurements are critical.

How many ml in a teaspoon?

US teaspoon = 4.929 mL (exactly 1/3 US tablespoon = 1/6 US fl oz). Metric teaspoon = 5 mL (used in medical dosing and international). One major reason medical dosing worldwide has switched to 5 mL ≡ metric teaspoon: household teaspoons vary enormously (ranging 3–9 mL in consumer studies), making them unsafe for pharmaceutical dosing. Always use a calibrated 5 mL syringe or measuring spoon for medicines.

How do I convert cubic meters to liters?

Multiply by 1,000 (exactly). \(1\,\text{m}^3 = 10^3\,\text{L} = 10^6\,\text{mL}\). This follows directly from the SI definition: 1 L = 1 dm³ = 0.001 m³. Reverse: divide litres by 1,000 to get cubic metres. Example: a 5,000 L water tank = 5 m³. A 50 m³ concrete pour = 50,000 L.

How many cubic feet in a gallon?

1 US gallon = 0.133681 ft³ (or 7.48052 US gallons per cubic foot). Derivation: 1 US gal = 231 in³; 1 ft³ = 1,728 in³; therefore 1 gal/ft³ = 231/1,728 = 0.133681. Useful in HVAC and plumbing: a pipe with 1 ft diameter, 1 ft long ≈ 0.7854 ft³ ≈ 5.875 US gallons of capacity. UK gallons per cubic foot: 1 ft³ = 6.2288 UK gal.

What is a petroleum barrel (bbl)?

1 petroleum barrel = 42 US gallons = 158.987 L (exact: 42 × 3.785411784 L). Established 1872 by Pennsylvania oil producers using the standard wooden barrel. The international crude oil market uses barrels/day (b/d) as its primary flow rate measure. Note: beer barrel (US) = 31 gal; wine barrel = 59 gal; US dry barrel = 105 dry quarts ≈ 115.6 L — different from petroleum barrel.

What is an acre-foot?

1 acre-foot = 43,560 ft³ = 1,233.48 m³ = 325,851 US gallons. The volume of water that covers 1 acre (43,560 ft² = 4,047 m²) to a depth of 1 foot. Used for reservoir capacity, irrigation water rights, and groundwater depletion in US water law. Lake Mead (US/Nevada), the largest US reservoir by capacity, holds about 36.7 km³ ≈ 29.7 million acre-feet when full. California allocates water rights in acre-feet per year.

How many tablespoons are in a cup?

US: 16 tablespoons = 1 cup = 236.588 mL. Therefore 1 US tbsp = 236.588/16 = 14.787 mL. Metric: 250 mL ÷ 15 mL/tbsp = 16.67 tablespoons per metric cup (not a clean whole number — a reason professional metric recipes avoid tablespoon-based cup divisions). 48 US teaspoons = 1 US cup. 3 tsp = 1 tbsp in all common systems.

What is the difference between a dry gallon and a liquid gallon (US)?

US dry gallon = 268.8025 in³ = 4,404.88 mL — used for dry goods (grain, fruit). US liquid gallon = 231 in³ = 3,785.41 mL — used for fluids. The dry gallon (1/8 of a US Winchester bushel) is about 16.3% larger than the liquid gallon. In practice, the dry gallon is rarely used; dry goods are now sold by weight (kg or lb) rather than volume, making the distinction largely historical.

How accurate is the Num8ers Volume Conversion Calculator?

Uses exact legal factors: 1 US gal = 231 in³; 1 in = 25.4 mm (both exact, 1959 international agreement) → 1 US gal = 3,785.411784 mL exactly. 1 UK gal = 4,546.09 mL (UK Weights & Measures Act 1985, exact). All metric prefixes are powers of 10 (exact). Cooking units: metric tbsp = 15 mL exact; US tbsp = ½ US fl oz = 14.786764... mL (through the gallon chain). JavaScript double precision: ~15 significant decimal digits — more than adequate for any practical application.

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