What this calculator does
Bean bag beads are expanded polystyrene at roughly 20 kg per cubic metre, which is very light: a bag 70 by 60 by 50 cm holds 0.21 cubic metres and needs about 4.2 kg of filler.
Filler is sold by volume rather than weight, usually in bags of 100 litres, which is where the confusion starts. Working in mass and then converting is the reliable route, and it is worth buying slightly more than calculated since beads compress over time and most bean bags need topping up within a year or two.
The formula
The volume is the three dimensions multiplied together and converted to cubic metres. The filler mass is that volume multiplied by 20 kg per cubic metre, the typical bulk density of expanded polystyrene beads. The bags to buy figure divides the volume by the bag size and rounds up.
| Term | Meaning |
|---|---|
| Expanded polystyrene (EPS) | The standard bean bag filler: light, compressible and cheap. |
| Bulk density | About 20 kg per cubic metre for loose beads, though it varies with bead size and grade. |
| Compression | Beads pack down with use, which is why bean bags need topping up. |
| Fill level | Most bean bags are filled to about two thirds to allow the shape to form around the user. |
The inputs explained
| Field | What to enter |
|---|---|
| Filled length (cm) | Bag length in centimetres. |
| Filled width (cm) | Bag width in centimetres. |
| Filled height (cm) | Bag height in centimetres. |
| Filler bag size (kg/bag) | Filler bag size in kilograms, for the bags-to-buy figure. Beads are usually sold by volume, so convert first: 100 litres of beads weighs about 2 kg. |
When to use it
Filling a new bean bag cover
Covers are frequently sold without filler, and the quantity needed is not printed on them.
Topping up a flattened bag
Beads compress over a year or two and the bag loses its shape. Topping up is cheaper than replacing and the calculation gives a starting quantity.
Making a bag from scratch
Working from the intended dimensions rather than from a purchased cover, where the filler quantity has to be estimated in advance.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much filler does each bag size need?
Three bean bag sizes with the filler quantity each needs.
| Filled length | Filler needed | Filled volume | Bags to buy |
|---|---|---|---|
| 60 cm | 3.60 kg | 0.180 m³ | 2 |
| 70 cm | 4.20 kg | 0.210 m³ | 3 |
| 90 cm | 5.40 kg | 0.270 m³ | 3 |
Questions
How much filler does a bean bag need?
Roughly 20 kg per cubic metre of bag volume, so a typical adult bean bag of about 0.2 cubic metres takes around 4 kg. Filler is commonly sold in 100 litre bags, which at that density is about 2 kg each, so a bag that size takes two to three of them.
Should I fill it completely?
No, about two thirds full is usual. A fully packed bean bag is rigid and does not mould around you, which is the entire point of it. Leaving room for the beads to move is what makes it comfortable.
Why does a bean bag go flat?
The beads compress under repeated use, losing volume permanently. Most bean bags need topping up within one to two years of regular use. Buying slightly more filler than calculated at the outset saves a second order later.
Is there an alternative to polystyrene beads?
Shredded memory foam is the main one. It is considerably heavier and more expensive but does not compress the same way, so it holds its shape far longer. The density is completely different, so the 20 kg per cubic metre figure here does not apply to it.
For estimating boxes for a move, see the moving boxes calculator. For tent sizing, see the tent size calculator.