The bean bag filling calculator above answers the question that every empty cover raises: how many litres of beads does this actually take? It works from the geometry of the shape you choose, applies the fill level you set rather than a hidden assumption, and adds an allowance for the settling that turns a new chair into a flat one within a year. It then converts to cubic feet and to the number of bags you would need to buy.
Arb Digital builds free calculators that keep every assumption editable and say where the maths comes from. Filler volume is a place where confident-sounding round numbers do real damage, because ordering too little means a second delivery charge and ordering too much means a bag of loose polystyrene beads you now have to store.
What This Bean Bag Filling Calculator Does
You pick one of four shapes — round, pear, cylinder or box — and give the dimensions of the empty cover. The calculator computes the volume that shape would enclose if it were filled solid, then multiplies by your fill percentage to get the working volume, then adds your settling allowance on top.
The headline is that final figure in litres. Alongside it you get the cover's full volume, so the difference between "how big is the chair" and "how much do I buy" is visible, the same figure in cubic feet for suppliers who sell that way, an approximate weight if you supply a bulk density, and the number of bags at the size you are buying, rounded up.
The bars underneath show the three quantities side by side: the cover's full volume, the working fill, and the total order including settling. Seeing them together is the point — the order is usually well below the cover's nominal volume, and people who assume otherwise consistently over-buy.
How to Use It
- Choose the shape that matches your cover and switch the units to centimetres or inches, whichever your tape measure gives you.
- Measure the empty cover laid flat and squared up, not a filled chair, which will have bulged into a different shape.
- Set the fill level. Two thirds is a reasonable default; go higher for a firm supportive chair and lower for a soft, slouchy floor bag.
- Set a settling allowance. Ten per cent covers the first year for most polystyrene bead fills; heavier daily use warrants more.
- Enter the bulk density and bag size from the product you are buying to get a weight and a bag count. Leave density at zero if you only want volume.
The Formula: How It's Calculated
Each shape uses its standard volume formula, and both of the awkward ones are worth stating explicitly.
A round bag is a sphere: V = (4/3)πr³, the relation Archimedes derived and which Wolfram MathWorld sets out on its sphere reference page. A cylinder is V = πr²h, and a box is length × width × height.
A pear or teardrop bag is treated as a conical frustum — a cone with its point cut off — which MathWorld gives on its conical frustum page as V = (1/3)πh(R&sub1;² + R&sub1;R&sub2; + R&sub2;²), where R&sub1; and R&sub2; are the base and top radii. That is a better fit for the classic tapered chair than a cone or a cylinder, both of which are off by a large margin.
From there: fill volume = cover volume × fill %, and order volume = fill volume × (1 + settling %).
Work the defaults through. A round bag 90 cm across has a radius of 0.45 m, so its volume is (4/3) × π × 0.45³ = 0.3817 m³, or 381.7 litres. At 66% fill that is 251.9 litres of working volume, and a 10% settling allowance brings the order to 277.1 litres. That is 9.79 cubic feet, about 3.3 kg at a bulk density of 12 kg/m³, and three 100 litre bags.
Why a Bean Bag Must Be Underfilled
The fill percentage is the field people get wrong, almost always by setting it too high, and the reason is worth understanding rather than accepting on trust.
A bean bag supports you because the beads flow out from under your weight and pile up around you. That flow needs somewhere to go. A cover packed to 95% has no spare volume, so the beads cannot move; the chair becomes a hard sphere that you sit on top of rather than in. It also puts the seams under constant tension, which is the usual cause of a split.
Underfill too far and the opposite happens: you sink through to the floor, and the chair offers no support at the hips at all. The workable band is roughly 60% to 80%, and where you sit inside it is a genuine preference rather than a right answer. A gaming or reading chair that has to hold a posture wants the top of that band. A floor bag you sprawl on wants the bottom.
One practical consequence: fill in stages. Add about half the calculated volume, sit in it, add more, sit again. The right amount is far easier to find by feel than by measurement, and the calculator's job is to tell you roughly how much to have on hand, not to be obeyed to the litre.
Settling, and Why Chairs Go Flat
Expanded polystyrene beads are mostly air held in thin-walled cells. Under repeated compression those cells collapse, and the bead's effective volume drops permanently. This is not a defect; it is what the material does.
The visible effect is a chair that feels excellent for a few months and then noticeably flat, usually in the seat where the load is concentrated rather than uniformly. The fix is a top-up, and buying the top-up with the original order is cheaper and simpler than a second delivery of a low-density, high-volume product later.
Fill type changes the rate substantially. Virgin polystyrene beads settle more slowly than recycled ones. Shredded memory foam does not settle in the same way at all, but it does compress and it is far heavier per litre — which is why the density field is an input rather than a constant, and why the weight estimate can move by a factor of ten between fills. If you want to work in the other direction, from a known weight to a volume, our density calculator handles that relation directly and the weight converter deals with any unit mismatch on the bag's label.
Measuring an Empty Cover Accurately
Most of the error in a filler estimate comes from the measurement, not the formula. Three habits help.
Measure the cover flat and squared, not a filled chair. A filled bean bag has already deformed under its own weight, so measuring its widest point overstates the diameter considerably.
For a round cover, the honest way to get a diameter is from the flat width. A sphere's cover laid flat gives you roughly half its circumference, so diameter is approximately twice the flat width divided by pi. Measuring across a bulging chair with a tape will give you a number several centimetres too large, and volume goes as the cube of that error — a 10% overestimate of diameter becomes a 33% overestimate of volume.
For a pear shape, measure the base and top diameters and the vertical height separately, and resist the temptation to measure the sloping side as the height. If you want to check a single shape's volume in isolation, our sphere volume calculator and cylinder volume calculator do exactly that, and the volume converter will move between litres, cubic feet and cubic metres if your supplier quotes a unit this page does not.
Buying: Bags, Cubic Feet and the Inner Liner
Filler is sold by volume in a confusing variety of units. Litre-based bags are common in Europe, cubic-foot boxes in North America; the calculator gives both so you can compare like with like. One cubic foot is about 28.3 litres.
The bag count is rounded up, which is deliberate. Running slightly over is a top-up; running slightly under means the chair is unusable until another order arrives.
Finally, if your cover does not have an inner liner, get one. Filling a single-skin cover means every future wash empties the chair, and a zip failure empties it onto the floor. Beads are close to impossible to sweep and behave like a fluid on hard floors. Fill outdoors or in a bath, and cut the corner off the filler bag rather than opening it fully — static makes loose beads travel.
Arb Digital designs and builds free interactive calculators that state their formulas, take the reader's own measurements, and earn links because they are genuinely useful. Browse what we have already published, or tell us what your audience keeps searching for.
Browse the Free Tools Hub Talk to Arb DigitalCommon Mistakes to Avoid
- Measuring a filled chair. It has already bulged. Measure the empty cover laid flat, or your volume will be far too high.
- Filling to 90% or more. The beads then cannot move, so the chair is hard rather than supportive, and the seams are under permanent load.
- Ignoring settling. Polystyrene beads compress permanently with use. A chair with no top-up allowance will feel flat within months.
- Assuming all fills weigh the same. Shredded foam is many times heavier per litre than polystyrene beads. Use the density from the bag you are actually buying.
- Filling a cover with no inner liner. Every wash then empties the chair, and there is no second barrier if the zip fails.
Related Free Tools From Arb Digital
Check a single shape with the sphere volume calculator or the cylinder volume calculator, convert supplier units with the volume converter or the length converter, and work between weight and volume with the density calculator and the weight converter. If you are planning the floor space the finished chair will take, the square footage calculator helps. Everything else is on the free online tools hub.
Frequently Asked Questions
It depends on the cover's volume and how firmly you want it filled. The calculator computes the cover's volume from its shape and dimensions, then applies your chosen fill percentage. As an illustration, a 90 cm round cover holds about 382 litres when solid, so a two-thirds fill plus a ten per cent settling allowance is about 277 litres.
Because the beads have to be able to move. They flow out from under your weight and pile up around you, and that is what makes the chair supportive. A cover packed full has no spare volume, so it becomes a hard ball you sit on rather than in, and the seams stay under constant tension.
Around ten per cent covers the first year for most polystyrene bead fills, and heavier daily use warrants more. Beads are mostly air in thin-walled cells, and repeated compression collapses those cells permanently, so the chair loses volume over time and needs topping up.
Lay it flat rather than measuring a filled chair. A sphere's cover laid flat gives roughly half its circumference, so the diameter is about twice the flat width divided by pi. Accuracy matters here because volume goes as the cube of the diameter, so a ten per cent error becomes a thirty-three per cent error in volume.
That depends entirely on the fill, which is why bulk density is an input rather than a fixed constant. Expanded polystyrene beads are very light, while shredded foam is many times heavier per litre. Use the density printed on the bag you are buying, or leave the field at zero to skip the weight estimate.
One cubic foot is about 28.3 litres, and the calculator reports both units so you can compare products sold either way. The bag count is rounded up on purpose, since running slightly over gives you a top-up while running under leaves the chair unusable.
It is strongly worth having. Without one, washing the cover means emptying the whole chair, and a zip failure releases loose beads onto the floor with no second barrier. Beads behave like a fluid on hard surfaces and are very difficult to sweep up.
This page estimates volume from geometry and the figures you supply; it is not product guidance. Loose polystyrene beads are a recognised choking and suffocation hazard for young children, so fill away from them, keep zips closed and secured, and follow the safety information supplied with your own cover and filler.
