Quick answer
Barrel volume ≈ π × L × (2D² + d²) ÷ 12, where D is the bung (middle) diameter, d the head diameter and L the inside length. A barrel with 22 in heads, 28 in bung and 36 in length holds about 83.72 US gallons (316.9 litres).
Enter the head diameter, the bung diameter and the inside length. The calculator returns capacity in gallons, litres and cubic inches.
Related tools: Volume Converter: Convert litres, gallons, cups, spoons and more.
How to use the Barrel Volume Calculator
- Enter head diameter (in) (above 0).
- Enter bung (middle) diameter (in) (above 0).
- Enter inside length (in) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Head diameter | A number, in in | > 0 |
| Bung (middle) diameter | A number, in in | > 0 |
| Inside length | A number, in in | > 0 |
Formula and method
Formula
V ≈ π × L × (2D² + d²) ÷ 12 (D = bung, d = head)
IEEE-754 double precision; shown to the decimals indicated.
A classical approximation for a barrel with parabolic staves; use inside measurements.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Head diameter = 22; Bung (middle) diameter = 28; Inside length = 36.
| Result | Value |
|---|---|
| Capacity | 83.72 gal |
| In liters | 316.9 |
| In cubic inches | 19,340 |
Example 2
Inputs: Head diameter = 18; Bung (middle) diameter = 24; Inside length = 30.
| Result | Value |
|---|---|
| Capacity | 50.18 gal |
| In liters | 190 |
| In cubic inches | 11,592 |
Example 3
Inputs: Head diameter = 16; Bung (middle) diameter = 20; Inside length = 28.
| Result | Value |
|---|---|
| Capacity | 33.51 gal |
| In liters | 126.9 |
| In cubic inches | 7,741 |
The first line is the headline result (capacity). Below it the barrel Volume Calculator lists in liters and in cubic inches, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
The approximation
The formula treats the barrel as a parabolic spindle, which is a good approximation of the curved staves. For the example: π × 36 × (2 × 784 + 484) ÷ 12 = π × 6,156 ≈ 19,340 in³, and 19,340 ÷ 231 = 83.72 gallons.
Where it can mislead
Real barrels vary in curvature, and measurements are to the inside. A 'standard' US whiskey barrel is 53 gallons and a wine barrel 59 gallons, so the example is a large barrel.
How the result changes with head diameter
Holding every other input at the first worked example, this table changes only head diameter. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Head diameter | Capacity | In liters | In cubic inches |
|---|---|---|---|
| 11 | 68.91 gal | 260.9 | 15,918 |
| 22 | 83.72 gal | 316.9 | 19,340 |
| 44 | 142.96 gal | 541.2 | 33,024 |
| 88 | 379.93 gal | 1,438.2 | 87,764 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Head diameter: entering "0" shows "Head diameter must be greater than 0." beside that field and no result.
- Inside length: entering "0" shows "Inside length must be greater than 0." beside that field and no result.
Choosing between the Barrel Volume Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Volume Converter](/converters/volume-converter/) | value, from and to | US gallon → Litre (L) |
| [Aquarium Volume Calculator](/construction/aquarium-volume/) | length, width and water height | Capacity |
| [Pool Volume Calculator](/construction/pool-volume-calculator/) | shape, length and average depth | Pool volume |
| [Cylinder Volume Calculator](/math/cylinder-volume-calculator/) | radius and height | Volume |
| [Sphere Volume Calculator](/math/sphere-volume-calculator/) | radius | Volume |
Assumptions and limitations
- An approximation of ±1–2%
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for head diameter and inside length to confirm this.
Frequently asked questions
How do I measure inside length?
Between the inner faces of the heads.
Is a US gallon assumed?
Yes, 231 cubic inches.
How accurate is it?
Usually within a few percent.
What does the Barrel Volume Calculator calculate?
Approximate capacity of a barrel from head diameter, bung diameter and length. It returns Capacity, In liters and In cubic inches.
What formula does the Barrel Volume Calculator use?
V ≈ π × L × (2D² + d²) ÷ 12 (D = bung, d = head). A classical approximation for a barrel with parabolic staves; use inside measurements.
What do I need to enter in the barrel Volume Calculator?
You enter Head diameter (in), Bung (middle) diameter (in) and Inside length (in).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. An approximation of ±1–2%.
What is an example of a barrel Volume result?
With head diameter 22, bung (middle) diameter 28 and inside length 36, the capacity is 83.72 gal.
Where does the method come from?
The method follows: Oughtred's barrel formula (classical gauging approximation).
Related calculators
- Volume Converter — Convert litres, gallons, cups, spoons and more.
- Cylinder Volume Calculator — Volume of a cylinder.
- Sphere Volume Calculator — Volume and surface area of a sphere.
- Volume of a Hemisphere Calculator — Volume and surface area of a hemisphere.
- Cartesian to Polar Converter — Radius and angle from x and y.
- Polar to Rectangular Converter — x and y from radius and angle.
- Pie Chart Calculator — Shares and slice angles for a set of values.
Sources
- Oughtred's barrel formula (classical gauging approximation)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.