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Tank Volume Calculator: Capacity and Fill Level

Work out the capacity of a cylindrical, rectangular or capsule tank in gallons and liters, and how much is in it at a given fill level. Pick a vertical or horizontal cylinder, a rectangular, capsule or cone-bottom tank, or a pipe run, enter the inside size and a dipstick reading, and get gallons, liters, cubic feet and the weight.

Your numbers

Measure inside the wall, or take the outside and subtract twice the wall thickness.

Capsule: overall height, including the rounded ends.

lb/gal

Water is 8.34 lb per gallon. For another liquid, use its specific gravity × 8.34, or the density on its data sheet.

Tank capacity

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In liters
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In cubic feet
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In cubic meters
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Weight of the liquid
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Inside measurements give the liquid capacity. Dished or flat heads, fittings and a sloped floor change the real figure; the tank maker's chart wins.

An estimate from your measurements.

The calculation runs in your browser and ParrotNotes does not store your numbers. They sit in the page address so you can bookmark or share the result.

How to calculate tank volume

Measure the inside of the tank, pick its shape and use the matching formula. A round tank standing up is π × (diameter ÷ 2)² × height; the same tank lying on its side uses the length instead of the height. A rectangular tank is length × width × height. Work in inches and divide the cubic inches by 231, because NIST defines the US gallon as 231 cubic inches (3.785411784 liters).

Worked example: a vertical tank 48 inches across and 60 inches tall holds π × 24² × 60 = 108,573 cubic inches, which is 470.0 gallons, 1,779 liters or 62.8 cubic feet. With 45 inches of liquid in it, it holds 352.5 gallons and is 75% full: in a straight-sided tank standing up, the depth and the volume rise together.

Horizontal tank volume at a partial fill

A cylinder on its side is the shape where a quick guess goes wrong. The liquid's end face is a circular segment, so the first inches at the bottom hold little and the middle inches hold the most. The calculator uses the segment area from Wolfram MathWorld, r² × acos((r − h) ÷ r) − (r − h) × √(2rh − h²), times the length.

Take a tank 48 inches across and 72 inches long: 564.0 gallons full. At 24 inches of liquid it is exactly half full, 282.0 gallons. At 12 inches, a quarter of the height, it holds 110.3 gallons, only 19.6% of the tank. Pick By liquid height, type the dipstick reading and read the gallons, the percent full and the room left for a delivery.

Capsule and cone-bottom tanks

A capsule tank is a cylinder with a rounded end on each side. Enter the diameter and the overall length (or height) end to end; the calculator takes the straight part as a cylinder and the two rounded ends together as a sphere. A horizontal capsule 4 ft across and 10 ft long holds 814.7 gallons; at 1 ft of liquid, 149.4 gallons.

A cone-bottom tank, common for fermenters, chemical day tanks and hoppers, is a cylinder standing on a cone with its point down. Enter the diameter, the straight wall height and the cone height, and measure the liquid from the tip. A tank 48 inches across with a 60-inch wall and a 24-inch cone holds 532.7 gallons, but only 7.8 gallons when the liquid is 12 inches up the cone.

Pipe volume calculator: a pipe or hose run

To fill, flush, treat or drain a line, you need what the pipe holds. Pick Pipe and enter the inside diameter and the length of the run: volume = π × (inside diameter ÷ 2)² × length. A 2-inch inside diameter holds about 0.163 gallons a foot, so a 100 ft run holds about 16.3 gallons (61.8 liters).

Use the inside diameter, not the nominal size printed on the pipe: wall thickness differs by material and schedule, and the maker's table gives the real figure. For a run with several sizes, work out each length and add them.

Weight of the liquid

A gallon of water weighs about 8.34 pounds and a liter about 1 kilogram, the figures on the California State Water Resources Control Board's operator formula sheet. That makes the 470-gallon tank above about 3,920 pounds of water before the tank itself, which matters for a stand, a truck bed or a floor.

For another liquid, the same sheet gives specific gravity = the liquid's weight per gallon ÷ 8.34. Turn it around: weight per gallon = specific gravity × 8.34, with the specific gravity from the product's safety data sheet. Type that into Liquid weight.

Measure the inside, then check the maker's chart

The formulas assume clean shapes. Real tanks have dished or flat heads, fittings, baffles and floors that slope to a drain, so the maker's capacity chart (a strapping or dipstick chart) beats any formula when you have it. Oval and obround heating oil tanks are not cylinders: use the chart for those.

Measure inside the wall where you can. From outside, subtract twice the wall thickness from the diameter. Check the result against the nameplate capacity: if they disagree by more than a few percent, a measurement is off.

For reps who sell what goes in the tank

Chemical, industrial and beverage reps get asked the same thing on site: how much will it take to fill this, and how much is in it now. The tank's size turns a visit into an order quantity, a delivery schedule and a quote for totes or bulk.

The rest of the visit is what the customer says: how often they run out, which product they use for what, what went wrong with the last delivery, who signs off. Those notes decide the next order as much as the gallons do.

Sources, checked October 2026. All results are estimates:

More for chemical, industrial and beverage reps: Chemical sales rep, Industrial sales, Wine sales rep.

The gallons are on the page; the order is in the conversation

On a plant visit or a call with the buyer, the customer tells you what runs through the tank, how often it is refilled, what went wrong with the last delivery and when they want the next one. Record the visit in ParrotNotes and get a summary and next steps, so the quote and the order match what they asked for.

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Tank volume calculator FAQ