Volume of a cylinder in gallons

Contents

1. The formula for cylinder volume in gallons
2. How to calculate gallons in a cylinder, step by step
3. Worked examples
4. Cylinder capacity chart in US gallons
5. Gallons per inch of height: reading a vertical tank
6. US gallons vs imperial gallons
7. Gallons, cubic feet, liters and weight
8. Common mistakes when you calculate cylinder volume in gallons
9. Related capacity calculations
10. FAQ

The calculator above takes a radius or a diameter and a height in inches, feet, centimeters or meters and returns the capacity in US gallons, with imperial gallons, liters and cubic feet beside it. The rest of this page explains each step, so you can calculate gallons in a cylinder by hand and check any result.

The formula for cylinder volume in gallons

A gallon is a volume, so the method has two parts. First find the volume of the cylinder in cubic units with the standard cylinder volume formula, V = πr²h. Then convert those cubic units to gallons with an exact factor.

The number 231 is not a rounded value: the US gallon is defined as exactly 231 cubic inches. A cubic foot is 12 × 12 × 12 = 1,728 in³, and 1,728 ÷ 231 = 7.48052 gallons. That is why the inch route uses a division and the foot route a multiplication.

Shortcuts with the diameter

Most people measure straight across a tank or a pipe, which gives the diameter. Since r = d ÷ 2, the formula becomes π × d² × h ÷ 4, and the constants can be folded into a single factor:

• Inches: gallons = d² × h × 0.0034. The exact factor is π ÷ 4 ÷ 231 = 0.0033999…, so 0.0034 is correct to four figures.
• Feet: gallons = d² × h × 5.875. The exact factor is π ÷ 4 × 7.48052 = 5.87519…, so 5.875 is also correct to four figures.
• With the radius: gallons = r² × h × 0.0136 in inches, or r² × h × 23.50 in feet.

For example, a tank 3 ft across and 4 ft tall gives 3² × 4 × 5.875 = 211.5 gallons; the full formula gives 211.51. For imperial gallons with inches, the diameter factor is 0.002831.

How to calculate gallons in a cylinder, step by step

1. Measure the insideTake the inside diameter and the inside height (or the depth of liquid, if you want the gallons actually present). Walls take up room, so outside measurements overstate the capacity.
2. Use one unitConvert both measurements to inches, or both to feet. Never multiply a radius in inches by a height in feet.
3. Find the radiusHalve the diameter: r = d ÷ 2.
4. Compute the volumeMultiply π by r squared, then by h. The result is in in³ or ft³.
5. Convert to gallonsDivide cubic inches by 231, or multiply cubic feet by 7.48052.

Worked examples

Example 1: a cylinder measured in inches

A container is 10 in across and 14 in tall. The radius is 5 in, the base area is π × 5² = 78.54 in², and the volume is 78.54 × 14 = 1,099.56 in³. Divide by 231: 4.760 US gallons. In imperial gallons that is 1,099.56 ÷ 277.419 = 3.964, and in liters 18.02 L.

Example 2: a tank measured in feet

A vertical tank is 3 ft across and 5 ft tall. The radius is 1.5 ft, the base area is π × 1.5² = 7.0686 ft², and the volume is 7.0686 × 5 = 35.343 ft³. Multiply by 7.48052: 264.38 US gallons, or 220.15 imperial gallons. The same tank holds 1,000.8 L, almost exactly one cubic meter.

Example 3: diameter in inches, height in feet

A drum is 18 in across and stands 4 ft tall. Convert the height first: 4 ft = 48 in. The radius is 9 in, so V = π × 81 × 48 = 12,214.5 in³, and 12,214.5 ÷ 231 = 52.88 US gallons. If you forget to convert and multiply π × 81 × 4, you get 1,017.9 "cubic inch-feet", which divided by 231 gives 4.41 gallons: twelve times too small.

Example 4: from centimeters to gallons

A barrel measured at 50 cm across and 80 cm tall has V = π × 25² × 80 = 157,079.6 cm³ = 157.08 L. Divide by 3.785411784: 41.50 US gallons, or 34.55 imperial gallons (157.08 ÷ 4.54609). The cylinder volume in liters page covers metric measurements in millimeters, centimeters and meters in more detail.

Example 5: how tall for a given number of gallons?

You need 100 gallons in a cylinder 24 in across. One inch of height holds π × 12² ÷ 231 = 1.9584 gallons, so the height is 100 ÷ 1.9584 = 51.06 in. The same reasoning, solved for any unit, is on the page about the height of a cylinder.

Cylinder capacity chart in US gallons

Each value below is π × (d ÷ 2)² × h ÷ 231, computed with full-precision π and rounded to one decimal. Diameters and heights are inside measurements in inches; the heights 12 to 72 in are 1 to 6 ft.

The chart scales in a simple way. Gallons grow in proportion to the height, so a 10 ft tank holds ten times the 12 in value. They grow with the square of the diameter: the 24 in row is four times the 12 in row, and the 48 in row is sixteen times it.

Gallons per foot of height for large tanks

Gallons per inch of height: reading a vertical tank

In an upright cylinder, every inch of depth holds the same amount, because every horizontal slice is the same circle. Gallons per inch = π × r² ÷ 231, or d² × 0.0034 with the diameter. Once you know that number, a tape measure or a dipstick tells you the contents: multiply the depth of liquid by the gallons per inch.

Take a tank 36 in across. It holds 4.406 gallons per inch, or 52.88 gallons per foot. If the liquid stands 42 in deep (3.5 ft), the tank contains 42 × 4.406 = 185.07 gallons. This only works for a vertical cylinder with a flat bottom. A cylinder lying on its side holds more per inch near the middle than near the top and bottom; for that case use the cylinder tank volume calculator, which handles horizontal tanks and partial fills.

US gallons vs imperial gallons

Two different gallons are in common use, and confusing them changes the answer by about 20 %.

One imperial gallon equals 1.20095 US gallons. The US gallon is used in the United States; the imperial gallon is the one meant in older British and some Commonwealth measurements. When a result has to match a label, a quote or a regulation, check which gallon is meant before converting. The 3 ft × 5 ft tank of example 2 holds 264.38 US gallons but only 220.15 imperial gallons.

Gallons, cubic feet, liters and weight

Gallons are only one way to state a capacity. Builders and suppliers of fill, mulch or concrete usually work in cubic feet and cubic yards: the guide to the cubic feet of a cylinder covers measurements in feet and inches together and the conversion to cubic yards. Outside the US, the liter is the usual unit, with 1 L = 1,000 cm³.

Once you know the gallons, you can estimate the weight of the contents. Water at about 1,000 kg/m³ weighs roughly 8.345 lb per US gallon, so the 70.50 gallon cylinder from the introduction holds about 588 lb of water. For other liquids and for solid bars and tubes, the cylinder weight calculator multiplies the volume by the density of the material.

Common mistakes when you calculate cylinder volume in gallons

• Using the diameter in place of the radius. The radius is squared, so the answer comes out four times too large.
• Mixing inches and feet. Convert the height and the diameter to the same unit before multiplying, as in example 3.
• Dividing cubic feet by 231. The 231 factor applies to cubic inches only. Cubic feet are multiplied by 7.48052.
• Mixing up US and imperial gallons. The difference is about 20 %, far larger than any rounding error.
• Outside dimensions. For capacity, measure inside the walls. The difference matters most on small, thick-walled containers.
• Full height instead of liquid depth. To know how much is in a tank right now, use the depth of the liquid as h, not the height of the tank.
• Rounding π to 3.14. The result drops by about 0.05 %: negligible for a bucket, about 5 gallons on a 10,000 gallon tank.

Quick check: a cylinder 12 in across and 12 in tall holds about 5.9 gallons. Scale from there: double the height, double the gallons; double the diameter, four times the gallons.

Related capacity calculations

These pages take the same cylinder further, each with its own calculator and tables.

FAQ

How do I calculate the volume of a cylinder in gallons?

Measure the radius and the height in inches, compute π × r² × h to get cubic inches, then divide by 231. A cylinder 24 in across and 36 in tall holds π × 12² × 36 = 16,286 in³, which is 70.50 US gallons.

How do I find the gallons in a cylinder when the radius and height are in feet?

Compute π × r² × h in cubic feet, then multiply by 7.48052. With r = 2 ft and h = 5 ft: π × 4 × 5 = 62.832 ft³, and 62.832 × 7.48052 = 470.0 US gallons.

How do I find the volume of a cylinder in US gallons from the diameter and height?

With both in inches, multiply the diameter squared by the height and by 0.0034: gallons = d² × h × 0.0034. With both in feet, use gallons = d² × h × 5.875. Both factors come from π ÷ 4 and are accurate to four significant figures.

How many gallons are in a cubic foot?

One cubic foot holds 7.48052 US gallons (1,728 in³ ÷ 231 in³) or about 6.229 imperial gallons.

Is a US gallon the same as an imperial gallon?

No. A US gallon is 231 in³ (3.785411784 L); an imperial gallon is 4.54609 L, about 277.42 in³. The same cylinder holds about 20 % more US gallons than imperial gallons: one imperial gallon equals 1.20095 US gallons.

How many gallons does a cylinder hold per inch of height?

Gallons per inch = π × r² ÷ 231 with the radius in inches, or d² × 0.0034 with the diameter. A tank 36 in across holds 4.406 US gallons for each inch of liquid depth.

Related

• Volume in litersCylinder volume in liters: π × r² × h in cm, divided by 1,000. Convert from mm, cm or m, with worked examples and a table of liters per cm for common diameters.
• Cubic feetCubic feet of a cylinder = π × r² × h with r and h in feet. Mixed feet and inches, cubic inches ÷ 1,728, cubic yards and gallons, with a table per foot.
• Cylinder tank volumeTank volume calculator for vertical and horizontal cylinder tanks, full or partly filled. Get the capacity in gallons and liters, with worked examples.

Updated October 12, 2026