Storage Tank Volume Calculator: How to Find Capacity

This storage tank volume calculator works out the capacity of a tank in litres, US gallons, or cubic metres from its shape and dimensions. You enter the tank shape, the relevant measurements (diameter, length, width, height, or liquid depth), and the calculator returns the total volume and, for horizontal tanks, the volume of liquid currently inside. The result is given in multiple units so you can use it for sizing, filling, or transport planning.

Formula

The formulas depend on the tank shape. For a vertical cylinder, the total volume is the circular area times the height: V = π × (d/2)² × h, where d is the diameter and h is the height (or liquid depth). For a horizontal cylinder, the total volume is the same formula, but the liquid volume is more complex because the liquid surface is a chord of the circle: V_liquid = L × [r² × acos((r – h)/r) – (r – h) × sqrt(2rh – h²)], where r = d/2, L is the tank length, and h is the liquid depth. For a rectangular tank, volume is simply length × width × height: V = l × w × h.

All dimensions must be in the same unit. The calculator uses metres for input, but you can enter any unit as long as you convert consistently. The outputs are in cubic metres, litres, and US gallons. To convert: 1 m³ = 1000 L = 264.172 US gallons.

Worked Example

Take a horizontal cylinder with diameter d = 2 m, length l = 4 m, and liquid depth h = 1 m (the default values).

1. Calculate the radius: r = d/2 = 1 m.
2. Total volume: V_total = π × (1)² × 4 = 12.566 m³.
3. Liquid volume: V_liquid = 4 × [1² × acos((1-1)/1) – (1-1) × sqrt(2×1×1 – 1²)] = 4 × [1 × acos(0) – 0] = 4 × (π/2) = 6.283 m³.
4. Convert to litres: 6.283 m³ × 1000 = 6283 L.
5. Convert to US gallons: 6.283 × 264.172 = 1660 US gal.

The calculator shows total volume 12.57 m³, liquid volume 6.28 m³, 12566 L total, and 3320 US gal total. The liquid volume is half the total because the tank is half full.

When to Use This Calculator

Use this tool for any tank that is a cylinder (horizontal or vertical) or a rectangular box. Common applications include:

• Determining how much liquid a new tank can hold before installation.
• Estimating the amount of fuel, water, or chemical in a partially filled horizontal tank (e.g., a fuel storage tank or a water tank on a truck).
• Checking whether a tank meets regulatory or transport capacity limits.
• Planning the volume of a custom-built tank for a specific purpose.

The horizontal cylinder formula is especially useful for storage tanks that are not filled to the top, because the volume of a partially filled horizontal cylinder is not a simple proportion of the total – it depends on the chord area.

How to Read the Result

The first output is the total volume in cubic metres, which is the headline answer. The second output is the liquid volume (for a partially filled tank) in cubic metres. The next two outputs convert total volume to litres and US gallons. If you need imperial gallons, multiply the US gallon value by 0.8327 (1 US gal = 0.8327 imperial gal). The liquid volume in litres or gallons is not shown directly, but you can compute it by multiplying the liquid volume in m³ by 1000 or 264.172.

For a vertical cylinder or rectangular tank, the liquid volume is simply the total volume when the tank is full; when partially filled, it is the same formula with the liquid height substituted for the total height. The calculator does this automatically when you enter a liquid depth less than the full height.

Common Mistakes and Limitations

• Unit mix-ups: Entering diameter in inches and length in feet will give a wildly wrong answer. Convert all dimensions to the same unit first.
• Using the outside diameter instead of the inside: For wall thickness, use the inner diameter for liquid capacity. The calculator assumes the dimensions are internal.
• Horizontal cylinder liquid depth: The formula works for any liquid depth from 0 to the diameter. If h > d, the tank is overflowing; the formula still gives a result but it is not physically meaningful.
• Elliptical or other shapes: This calculator only handles cylinders and rectangular boxes. For spherical, elliptical, or conical tanks, you need a different formula.
• Rounding: The calculator rounds to 2 decimal places for m³, but the litre and gallon conversions are based on the unrounded value, so there may be slight differences if you do the conversion by hand.

The horizontal cylinder formula is exact for a perfect cylinder. It assumes the tank is level and the ends are flat. If the tank has dished or elliptical heads, the actual volume will be slightly larger – typically 5–10% depending on the head shape.

Choosing the Right Tank Shape

Select the shape that matches your tank. The three options cover the vast majority of storage tanks:

• Horizontal cylinder: Common for fuel, oil, and water storage on farms or industrial sites. The liquid volume calculation is the most complex because the liquid surface is a chord.
• Vertical cylinder: Often used for water towers or chemical storage. The liquid volume is a simple cylinder volume with the liquid height.
• Rectangular: Used for open-top tanks, basins, or custom containers. The volume is length × width × height.

If you have a spherical tank (e.g., a propane sphere), the volume is (4/3)πr³, but that is not included here. For a cone-bottom tank, you would need to add the cone volume separately.

Safety and Accuracy Notes

When using this calculator for actual storage, always double-check the dimensions with a tape measure or the manufacturer’s data sheet. Overestimating capacity can lead to overflow, while underestimating can cause insufficient supply. For hazardous liquids, consult the relevant safety regulations for fill limits – many tanks are not filled to 100% capacity to allow for expansion. The calculator gives the geometric volume, not the usable volume, which may be less due to internal fittings, baffles, or dip tubes.

For liquid depth measurement, use a calibrated dipstick or a level sensor. The formula assumes the tank is perfectly horizontal; if it is tilted, the volume will differ. For large tanks, even a small tilt can cause a significant error in the liquid volume reading.

Frequently Asked Questions

How do I calculate the volume of a horizontal cylinder tank?

Use the formula V = L × [r² × acos((r – h)/r) – (r – h) × sqrt(2rh – h²)], where L is the length, r is the radius (diameter/2), and h is the liquid depth. This gives the liquid volume. For total volume, use V = πr²L. The calculator does this automatically when you select “Horizontal cylinder”.

What is the difference between total volume and liquid volume?

Total volume is the full capacity of the tank when it is completely filled. Liquid volume is the amount of liquid actually in the tank at a given liquid depth. For a vertical cylinder or rectangular tank, liquid volume is simply the cross-sectional area times the liquid height. For a horizontal cylinder, it is the chord area times the length.

Can I use this calculator for an underground storage tank?

Yes, as long as the tank is a cylinder or rectangular box. The calculator works for any orientation. However, for underground tanks, you must use the internal dimensions and account for any manways or internal structures that reduce capacity. Also, be aware of regulatory requirements for leak detection and fill limits.

How do I convert cubic metres to litres?

Multiply the volume in cubic metres by 1000. For example, 2.5 m³ × 1000 = 2500 litres. To convert to US gallons, multiply by 264.172. The calculator provides these conversions automatically.

What if my tank has elliptical heads?

This calculator assumes flat ends. Elliptical or dished heads add a small volume – typically 5–10% of the total. To get an accurate total, you would need to add the head volume separately, which depends on the head shape and dimensions. For most practical purposes, the flat-end approximation is acceptable for estimating.

Why is the liquid volume not a linear function of depth for a horizontal tank?

Because the cross-section of the liquid is a circular segment, not a rectangle. As the liquid depth increases, the area of the segment increases non-linearly. Near the bottom and top, the volume changes slowly; in the middle, it changes faster. This is why you cannot simply take a percentage of the total volume based on depth.

Related

• Yards to Square Feet Calculator: How to Convert
• Cubic Meter to Square Feet Calculator
• Cone Bottom Tank Volume Calculator

sel shape | Tank shape | Horizontal cylinder=1, Vertical cylinder=2, Rectangular=3
in d | Diameter | m | 2 | 0
in l | Length / Height | m | 4 | 0
in h | Liquid depth | m | 1 | 0
out total | Total volume | m³ | (shape==1 ? pi * d^2 / 4 * l : shape==2 ? pi * d^2 / 4 * l : d * l * h) | 2
out liquid | Liquid volume | m³ | (shape==1 ? l * (d^2 / 4 * acos(1 - 2*h/d) - (d/2 - h) * sqrt(h * (d - h))) : shape==2 ? pi * d^2 / 4 * h : d * l * h) | 2
out litres | Total in litres | L | total * 1000 | 0
out gallons | Total in US gal | gal | total * 264.172 | 0