Volume Calculator Online: Liters to Gallons, mL to Cups and Tank Volume Made Easy

Published 1 November 2026 · By Sardar Zain, Founder of Orixiva · 12-minute read

Filling a fish tank, comparing fuel prices abroad, following an American recipe in a metric kitchen or ordering water for a pool: all of these need a quick, reliable volume calculator online. The tricky part is not the maths. It is knowing that a US gallon and a UK gallon are different sizes, and that a “cup” can mean 236.6 mL, 240 mL or 250 mL depending on who wrote the label.

This guide explains every common volume conversion in plain English, shows how to work out the volume of boxes, tanks and pools, and walks you through the free Orixiva volume converter. It runs in your browser on PC or phone, free and without login, and shows all 18 volume units at once.

Volume units at a glance

Volume measures how much space something takes up, or how much liquid a container holds. Three families of units are in daily use:

All of these are in the Orixiva converter, together with the oil barrel (42 US gallons), so you can move between any two in one step. The spelling “litre” (UK) and “liter” (US) mean the same unit.

How to convert liters to gallons

1. Decide which gallon you need. US recipes, fuel prices and product labels in the United States use the US gallon. The UK and some older references use the imperial gallon.
2. Divide the liters by 3.785 (US) or 4.546 (UK).
3. Round at the end. 20 L ÷ 3.785 = 5.28 US gallons, or 4.40 UK gallons.

Gallons to liters

Multiply instead: 5 US gallons × 3.785 = 18.93 L, and 5 UK gallons × 4.546 = 22.73 L. A 5-gallon water jug in the US holds about 19 liters.

US vs UK gallons, pints and fluid ounces

The US and UK share unit names but not sizes. This is the most common reason volume conversions go wrong:

Notice the twist: the UK pint and gallon are bigger, but the UK fluid ounce is smaller. That is because a UK pint has 20 fl oz and a US pint has 16 fl oz. A pint of milk in London (568 mL) is noticeably more than a pint in New York (473 mL).

mL to cups, tablespoons and teaspoons

• 250 mL = 1.06 US cups = 16.9 US tablespoons.
• 500 mL = 2.11 US cups = 16.9 US fl oz.
• 1 liter = 4.23 US cups = 33.8 US fl oz.
• 100 mL = 0.42 US cups = 6.76 US tablespoons.

Which cup is it?

There are three cups in common use, and the difference matters for baking:

For nutrition labels, the US FDA uses 1 cup = 240 mL, 1 tablespoon = 15 mL and 1 teaspoon = 5 mL. The Orixiva converter uses the exact US customary cup (236.588 mL), which is what most American recipes mean. For flour, sugar and butter, weight is more reliable than cups; our cups to grams chart and the cooking calculator handle that.

How to calculate the volume of a box, tank or pool

Many people searching for a volume calculator want to find out how much a container holds. Work out the volume with the right formula, then convert it:

Remember that a tank is rarely filled to the brim, and glass and gravel take up space in an aquarium. Use the result as the maximum. For concrete, soil and other building materials, the paint, tiles and concrete guide adds waste allowances.

Flowchart: choose the right volume unit

1. Start with your number and its unitRead the label, recipe or spec sheet carefully
2. Is it a gallon, pint, quart or fluid ounce?
   From the USUse US units (gallon 3.785 L)From the UKUse imperial units (gallon 4.546 L)
3. Is it a cup or spoon in a recipe?
   US recipeUS cup 236.6 mLLabel or metric recipe240 mL or 250 mL
4. Is it a size (length × width × height)?Multiply in one unit first, then convert cm³ or m³
5. Convert, then round only the final answerCheck the “1 unit = …” rate shown by the converter

Who uses which volume units?

• Most of the world uses milliliters and liters for drinks, fuel and cooking, and cubic meters for water bills and freight.
• The United States uses US gallons for fuel and milk, fluid ounces for drinks, and cups and spoons in recipes.
• The United Kingdom sells fuel in liters, beer and milk in imperial pints, and some people still quote fuel economy in miles per imperial gallon.
• Science and medicine use mL, liters and cm³ everywhere.

When a number comes from another country, check which family it belongs to before you convert. The flowchart above helps with that.

Fuel, drinks and oil barrels

Fuel prices per liter vs per gallon

To compare fuel prices, convert the price, not just the volume. A price of $3.50 per US gallon is $3.50 ÷ 3.785 = $0.92 per liter. A price of 1.80 per liter is 1.80 × 3.785 = 6.81 per US gallon. A 50-liter car tank holds 13.2 US gallons or 11.0 UK gallons. For running costs per kilometre, see EV vs petrol running cost.

Drinks and bottles

A 330 mL can is 11.2 US fl oz, a 500 mL bottle is 16.9 US fl oz and a 2-liter bottle is 67.6 US fl oz (about half a US gallon).

Oil barrels

Crude oil is traded in barrels of exactly 42 US gallons, which is 158.99 liters. 1,000 barrels a day is about 159 cubic meters a day.

Cubic feet, engine sizes and shipping containers

Cubic units appear wherever products are measured by size rather than by the liquid they hold. The volume converter handles all of them:

• Fridges: an 18 cubic foot fridge holds about 510 liters. Many European fridges are sold in liters, so this conversion helps when comparing models.
• Car boots and trunks: a 450-liter boot is 15.9 cubic feet.
• Engine size: 1,600 cc (cubic centimeters) is 1.6 liters or 97.6 cubic inches. A classic “350” American V8 has 350 cubic inches, which is 5.7 liters.
• Shipping: a standard 20-foot container has roughly 33 m³ of internal space, about 1,170 cubic feet. Freight is often priced per cubic meter.

For parcels, carriers often charge by size as well as weight. The dimensional weight guide shows how box volume affects shipping cost.

Liters to gallons conversion chart

How to use the free volume converter (step by step)

1. Open the volume converter. Go to the Orixiva volume converter. It opens on 1 liter to US gallons. Use the menu or search box to switch between the 14 converters.
2. Type a value or a calculation. Decimals, fractions (3/4), scientific notation (2.5e3) and products such as 60*30*35 all work, so the box doubles as a simple volume calculator.
3. Choose From and To units. Pick from milliliter, liter, cubic meter, cubic centimeter, cubic inch, cubic foot, US teaspoon, tablespoon, fluid ounce, cup, pint, quart and gallon, imperial fluid ounce, pint, quart and gallon, and oil barrel.
4. Read the result. It updates as you type, with both rates (1 L = 0.2642 US gal and 1 US gal = 3.785 L), the scientific form and a full-precision value.
5. Check the working. “How it was calculated” shows your value turned into liters, then into the target unit.
6. Compare all 18 units. A table shows the same volume in every unit, so US and UK gallons, cups and cubic feet appear together.
7. Save or share. Swap units, copy the result, download it as a TXT file or print it. Press Convert to keep a result in Recent conversions and export the list as CSV.

The converter works on PC, Mac, tablet and phone. It is free, needs no login or sign-up, and nothing is uploaded: every calculation happens in your browser.

Display options

Under Display options you can choose significant figures (1–15) or decimal places (0–12), standard, scientific or engineering notation, and whether to show a thousands separator. Use 3–4 significant figures for recipes and more for lab or engineering work.

How to convert volume in Excel or Google Sheets

For a column of values, the CONVERT function helps. In Microsoft’s CONVERT reference, the US gallon is “gal”, the imperial gallon is “uk_gal” and the liter is “l”. Google Sheets accepts most of the same codes.

Mistakes to avoid when converting volume

Mixing US and UK gallons

Using the wrong gallon creates a 20% error. A UK car’s “50 miles per gallon” is not the same as a US car’s 50 mpg.

Treating fluid ounces as weight

Fluid ounces measure volume. Ounces (oz) measure weight. Only for water are the two roughly the same; for oil, honey or flour they differ. See kg to lbs and weight conversion for weight units.

Forgetting to cube the length factor

1 m = 100 cm, but 1 m³ = 1,000,000 cm³. Measuring a box in centimeters and treating the result as liters without dividing by 1,000 gives an answer 1,000 times too big.

Measuring the outside of a container

Wall thickness reduces the inside volume. Measure inside dimensions for tanks, boxes and aquariums.

Related guides: how to convert units (all 14 converters), speed calculator online, pressure calculator online and square feet to square meters.