Capacity Calculator
Calculate volume capacity from length, width, and height. Great for boxes, tanks, containers, and any space where you need volume.
Capacity Calculator
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What the capacity calculator does
Capacity is how much a container can hold. This calculator finds the capacity of a rectangular space, a box, tank, or bin, from its length, width, and height, and gives the answer in litres.
Below is what capacity means, the equation behind it, why it applies to rectangular shapes, and a worked example.
How to use it
- Enter the length, width, and height of the space in millimetres.
- Press Calculate for the capacity in litres, or Reset to clear it.
What capacity is
Capacity is just the volume of space inside a container, expressed as how much it can hold. For a fluid it is the amount of liquid that fills the space; for a bin it is how much can be packed in. Volume and capacity describe the same quantity, with capacity being the everyday word for it when the point is what a container can take.
Knowing it answers practical questions: how many litres a tank holds, whether a box will take what you need to store, how much a container can carry. Because it depends on all three dimensions, a container that looks only a little bigger can hold a good deal more, since the increase multiplies across length, width, and height together.
The equation it uses
For a rectangular space, the volume is simply the three dimensions multiplied together, length times width times height:
volume = length × width × height
The calculator multiplies your three measurements and converts the result into litres. Because each dimension contributes as a direct multiplier, doubling any one of them doubles the capacity, and doubling all three multiplies it eightfold.
Why it is for rectangular spaces
This calculator treats the space as a rectangular box, with flat sides meeting at right angles, where the volume is a clean product of length, width, and height. That covers a great many real containers: crates, tanks, bins, drawers, and rooms are all close enough to boxes for this to give the right answer.
Shapes that are not boxes need their own formulas, because their volume is not a simple product of three sides. A cylindrical tank depends on its radius and height through the area of a circle, and an irregular vessel needs a method suited to its form. For the common case of a rectangular container, though, multiplying the three dimensions is exact, and that is what this tool does.
Units and precision
You enter the three dimensions in millimetres, and the calculator returns the capacity in litres, a natural unit for the volumes most containers hold. The conversion follows from the fact that a litre is a million cubic millimetres, so the product of three millimetre measurements is scaled down accordingly. The result is shown to several decimal places, finer than most measurements of a container warrant.
A worked example
Take a box measuring 500 millimetres long, 400 millimetres wide, and 300 millimetres high.
Its volume is 500 × 400 × 300 = 60,000,000 cubic millimetres. Since a litre is a million cubic millimetres, that is a capacity of 60 litres. A box only slightly larger in each direction would hold noticeably more, because the three increases multiply together.
Questions people ask
How do you calculate capacity?
For a rectangular container, multiply length by width by height. The result is the volume, which this calculator converts into litres.
What is the difference between capacity and volume?
They describe the same quantity. Volume is the amount of space; capacity is the everyday word for it when the focus is on how much a container can hold.
Does this work for round tanks?
No. It is for rectangular boxes, where volume is length times width times height. A cylindrical or irregular container has a different volume formula based on its own shape.
Why does a slightly bigger box hold so much more?
Because capacity multiplies all three dimensions. A small increase in each one compounds, so doubling all three dimensions multiplies the capacity eightfold.
References
A quick note on where this comes from. The volume of a rectangular box as length times width times height is basic geometry, and the litre and its relationship to cubic measures follow the US National Institute of Standards and Technology.
- National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (SI). https://www.nist.gov/pml/special-publication-811
- Encyclopaedia Britannica, Volume (geometry). https://www.britannica.com/science/volume-geometry
Bibek Lal Karna is a PhD student and graduate teaching assistant at the University of Mississippi, with deep interests in theoretical and gravitational physics. He is also the founder of NRCC and is strongly engaged in scientific teaching and communication. At Eon Tools, he reviews physics tools.