Oval Tank Volume Calculator: How to Find Gallons

This calculator works out the volume of an oval (elliptical) tank in gallons and litres. You enter the tank’s length, width, and height (or the two radii and length), and it returns the total volume in US gallons, litres, and cubic feet. The calculation uses the standard formula for an elliptical cylinder, which is the shape most oval tanks approximate.

Formula

The volume of an oval tank is calculated as the area of the oval end times the length of the tank. The area of an ellipse (the shape of the end) is π × a × b, where a and b are the semi-major and semi-minor axes (half the width and half the height). Multiply that area by the length to get the volume in cubic units, then convert to gallons or litres.

In symbols: V = π × (W/2) × (H/2) × L

• V = volume (cubic feet, then converted to gallons or litres)
• π ≈ 3.14159
• L = length of the tank (feet or metres)
• W = width of the tank at its widest point (feet or metres)
• H = height of the tank at its tallest point (feet or metres)

To convert cubic feet to US gallons, multiply by 7.48052 (1 cubic foot = 7.48052 US gallons). To convert cubic feet to litres, multiply by 28.3168 (1 cubic foot = 28.3168 litres). If you measure in metres, 1 cubic metre = 1000 litres, and 1 cubic metre = 264.172 US gallons.

Worked Example

Using the default values from the calculator: length = 6 ft, width = 3 ft, height = 2 ft.

1. Find the semi-axes: a = W/2 = 3/2 = 1.5 ft; b = H/2 = 2/2 = 1 ft.
2. Area of the oval end = π × 1.5 × 1 = 4.7124 ft².
3. Volume in cubic feet = 4.7124 × 6 = 28.2744 ft³.
4. Convert to US gallons: 28.2744 × 7.48052 = 211.5 gallons.
5. Convert to litres: 28.2744 × 28.3168 = 800.7 litres.

The calculator shows 211.5 gallons, 800.7 litres, and 28.27 ft³, matching the manual calculation.

When to Use an Oval Tank Formula

Oval tanks are common for water storage, fuel tanks on boats and RVs, and some aquariums. The elliptical cylinder formula gives a very close estimate for these tanks because most are built with a constant cross-section along their length. Use this calculator when you need to know capacity for filling, chemical dosing, or determining if a tank will fit a space.

If your tank is horizontal and only partially filled, the volume of liquid is not a simple fraction of the total – it depends on the fill height. For a partially filled horizontal oval tank, you need a more complex formula that integrates the elliptical segment area. This calculator gives the total capacity, not the content at a specific fill level.

How to Measure an Oval Tank Accurately

To get a reliable volume, measure the inside dimensions, not the outside. Wall thickness can add several percent to the volume if you use external measurements.

• Measure the length from the inside of one end to the inside of the other.
• Measure the width at the widest point, from inner wall to inner wall.
• Measure the height from the bottom to the top, inside.
• If the tank has dished or domed ends, the formula underestimates volume. Add the end-cap volume separately if you need high accuracy.
• For a tank that is not a perfect ellipse (e.g., oval with flat sides), the formula still works well as long as the cross-section is roughly elliptical.

Common Mistakes and How to Avoid Them

The most frequent error is mixing up the width and height. For a horizontal oval tank, the width is the horizontal span and the height is the vertical span. If you swap them, the volume is the same because multiplication is commutative, but the shape description changes – that matters if you later calculate fill levels.

Another common mistake is using the diameter instead of the radius. The formula uses half the width and half the height, not the full width and height. Forgetting to halve them will give a volume four times too large.

Unit mix-ups are also common. If you measure in inches, you must convert to feet before using the 7.48052 factor (1 ft = 12 in, so 1 ft³ = 1728 in³). If you measure in centimetres, convert to metres (1 m = 100 cm) before using the litre conversion.

Limitations and Accuracy

The elliptical cylinder formula assumes the tank is a perfect ellipse in cross-section and has flat ends. Real tanks often have rounded or dished ends, which add volume. For a tank with hemispherical ends, add the volume of a sphere of the same radius. For a tank with elliptical or torispherical ends, the added volume is more complex; consult tank manufacturer data if you need exact numbers.

Also, the formula gives the total volume to the brim. In practice, tanks are not filled completely – leave an air gap for expansion, especially for fuel or liquids that expand with temperature. For water tanks, fill to about 95% of capacity to allow for overflow.

Alternative Methods and Comparisons

If you do not have the dimensions, you can measure the tank’s capacity by filling it with a known volume of water and timing the flow, but that is impractical for large tanks. Another method is to use a dipstick chart from the manufacturer, which gives volume as a function of fill height – that is the most accurate for partial fills.

For rectangular tanks, the volume is simply length × width × height. For cylindrical tanks, it is π × r² × length. The oval tank formula is a middle ground – it gives more accuracy than a rectangular approximation but is simpler than a full partial-fill integration.

Frequently Asked Questions

How many gallons is a 6×3×2 oval tank?

Using the formula, a tank that is 6 ft long, 3 ft wide, and 2 ft high holds about 211.5 US gallons. That is the same as roughly 800 litres or 176 imperial gallons.

Is this formula for horizontal or vertical oval tanks?

The formula works for both orientations as long as you measure the length along the axis of the tank. For a horizontal tank, the length is the horizontal dimension; for a vertical tank, the length is the height. The volume is the same regardless of orientation.

What if my tank has rounded ends?

The formula assumes flat ends. If your tank has rounded or domed ends, add the volume of the end caps. For hemispherical ends, add (4/3)πr³ for each end. For other shapes, check the manufacturer’s data or measure the actual displacement.

Can I use this for an oval aquarium?

Yes, if the aquarium is a true oval cylinder. Many oval aquariums are actually rectangular with rounded corners – in that case, the rectangular formula is more accurate. Measure the inside dimensions and compare both results to see which fits better.

How do I convert the result to imperial gallons?

US gallons are different from imperial gallons. To convert from US gallons to imperial gallons, multiply by 0.832674. For example, 211.5 US gallons × 0.832674 = 176.1 imperial gallons.

Why does the calculator ask for width and height instead of radii?

Most people measure the full width and height of a tank, not the semi-axes. The calculator divides them by two internally, so you can enter the numbers you actually measured without doing extra math.

Related

• Pocket Calculator with Cover: What to Know
• Pocket Calculator Casio: How to Pick and Use One
• Pocket Calculator Font: What It Is & How to Get It

in L | Tank length | ft | 6 | 0
in W | Tank width | ft | 3 | 0
in H | Tank height | ft | 2 | 0
out gal | Volume (US gallons) | gal | (pi * L * (W/2) * (H/2)) * 7.48052 | 1
out l | Volume (litres) | L | (pi * L * (W/2) * (H/2)) * 28.3168 | 1
out ft3 | Volume (cubic feet) | ft³ | pi * L * (W/2) * (H/2) | 2