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Fuel Tank Capacity Calculator | Find Tank Volume From Dimensions

Calculate fuel tank capacity in gallons and litres from the tank's dimensions — rectangular or cylindrical — with partial-fill levels supported. Size tanks, check fuel remaining from a dipstick reading, and plan refuels.

Last updated: June 2026 · Free · No sign-up required

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Results

Enter values above and click Calculate to see your result instantly.

Quick reference

Tank (inches)ShapeCapacity
24 × 12 × 10Rectangular12.5 gal
30 long × 12 diaCylinder14.7 gal
40 × 20 × 12Oval32.6 gal
48 × 24 × 24Rectangular119.7 gal

info Fuel Tank Capacity Calculator

Free everyday calculator — enter your numbers and get an instant, accurate result.

info Private by design

Everything runs locally in your browser. No uploads, no accounts, no tracking.

info Works everywhere

Fully responsive and mobile-friendly — calculate on any device, any time.

info Educational

Includes the formula and step-by-step explanation so you understand the math, not just the answer.

Interpretation guide

VehicleTypical tank
Compact car10–13 gallons
Mid-size sedan / crossover14–18 gallons
Full-size pickup / SUV20–36 gallons
Semi truck (per side)100–150 gallons

lightbulb Worked example

Let's say you are using the Fuel Tank Capacity Calculator. Calculates fuel tank capacity in gallons and liters from its length, width/diameter and height. Enter the values that match your situation into the input fields and press calculate — using realistic numbers makes the result directly useful for you.

Result: The calculator instantly applies the formula Gallons = cubic inches ÷ 231. Rectangular: L × W × H; Cylinder: π × r² × L; Oval: π × (W/2) × (H/2) × L and returns the result with appropriate precision.

What this means: Read the result in the context of what you are measuring. The step-by-step breakdown lets you confirm the math and understand which input most affects the outcome.

Formula & methodology

Formula: Gallons = cubic inches ÷ 231. Rectangular: L × W × H; Cylinder: π × r² × L; Oval: π × (W/2) × (H/2) × L

The Fuel Tank Capacity Calculator is built on a well-established calculation method. It uses the formula Gallons = cubic inches ÷ 231. Rectangular: L × W × H; Cylinder: π × r² × L; Oval: π × (W/2) × (H/2) × L to turn your inputs into a reliable result. Calculates fuel tank capacity in gallons and liters from its length, width/diameter and height. The steps are shown on the page so you can follow the reasoning from input to output.

  1. Measure the tank's length, plus width and height (rectangular/oval) or diameter (cylinder), in inches.
  2. Multiply to get cubic inches: L × W × H for a box, π r² L for a cylinder.
  3. Divide by 231 — the cubic inches in one US gallon.

Worked example: a 24 × 12 × 10 in rectangular tank holds 2,880 in³ ÷ 231 = 12.5 gallons (47.2 L). A 30-inch cylinder with 12-inch diameter: π × 6² × 30 = 3,393 in³ = 14.7 gallons.

Authoritative source: timeanddate.com

Frequently asked questions

How do I calculate fuel tank capacity?
Enter the required values into the input fields and press the calculate button. The tool applies the formula Gallons = cubic inches ÷ 231. Rectangular: L × W × H; Cylinder: π × r² × L; Oval: π × (W/2) × (H/2) × L and returns the result with a short explanation of each step, so you can check the working yourself.
How many gallons is my gas tank?
The Fuel Tank Capacity Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Calculates fuel tank capacity in gallons and liters from its length, width/diameter and height. There is no limit on usage, and it works on any device.
Why does my tank hold less fuel than the calculated size?
Manufacturers' stated capacity is the theoretical volume; the usable capacity is lower because the filler neck, venting, the fuel pump pickup, and an expansion allowance for temperature changes reserve part of the tank. Additionally, irregular tank shapes and gauge calibration reduce what you can actually pump in. The calculator gives the geometric volume; expect 5–10% less usable.
How do I convert cubic inches to gallons?
Divide the volume in cubic inches by 231, since one US gallon equals exactly 231 cubic inches: a tank of 3,000 in³ holds about 12.99 gallons. The calculator computes the tank volume from its shape (L×W×H for rectangular, πr²×L for cylinders) and applies the ÷ 231 conversion automatically, also giving litres.
How do I work out how much fuel is left at a given level?
For a rectangular tank, multiply the length by width by the CURRENT fuel height instead of the full height. For a horizontal cylinder, the partial volume follows the circular-segment formula based on the fill depth. The calculator accepts a fill level and returns the fuel remaining at that level, which is how you turn a dipstick reading into gallons.
What does the Fuel Tank Capacity Calculator do?
Calculates fuel tank capacity in gallons and liters from its length, width/diameter and height. The calculator takes your inputs, applies the standard calculation, and returns a clear result so you can make an informed decision without doing the math by hand.
What formula does the Fuel Tank Capacity Calculator use?
The Fuel Tank Capacity Calculator applies the standard formula: Gallons = cubic inches ÷ 231. Rectangular: L × W × H; Cylinder: π × r² × L; Oval: π × (W/2) × (H/2) × L. The tool walks through each step of the calculation so you can verify the numbers yourself.
Is the Fuel Tank Capacity Calculator free and private?
Yes — the Fuel Tank Capacity Calculator. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.
How accurate is the Fuel Tank Capacity Calculator?
The Fuel Tank Capacity Calculator applies the standard formula: Gallons = cubic inches ÷ 231. Rectangular: L × W × H; Cylinder: π × r² × L; Oval: π × (W/2) × (H/2) × L. It is tested against published worked examples before launch and uses native double-precision arithmetic, so results are accurate to typical precision for the values you enter — with no intermediate rounding that could distort the answer.

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