Polyfill Stuffing Weight Calculator

Polyfill (polyester fiberfill) is sold by weight, not volume. To estimate how much you need, convert from your toy’s volume to grams based on how densely you want to fill it.

Density by firmness:

• Soft / floppy (teddy bears, decorative cushions): 10 g/L
• Medium (most stuffed animals, pillows): 20 g/L
• Firm (play balls, poseable toys): 35 g/L

The formula:

weight_g = volume_L x density_g_per_L

Getting the volume, which is the hard part. A bear is not a box. Measure the smallest box the finished toy would fit in, then multiply by a shape factor for how much of that box the toy actually occupies:

A 20 x 15 x 10 cm bear body box is 3 L. At the 0.65 factor that gives about 2 L of stuffable space, and at 20 g/L that is 39 g of polyfill.

Those factors are geometry, not guesswork: a sphere fills exactly π/6 of its bounding cube, which is 0.5236, and the 0.65 for a limbed body sits between that and a box because the torso is fat and the arms are not.

Practical notes

Polyfill compresses significantly when first stuffed and then relaxes over hours. Toys often feel slightly firmer right after stuffing and soften to their final feel overnight. If you want a consistently firm toy, stuff it 15-20% more than the calculation suggests and check the next day.

The number this page gives is the fill for an evenly stuffed toy. Real plush is not evenly stuffed: a head that has to hold its shape wants more, a floppy ear wants almost none, and a neck that needs to bend wants less than the head on either side of it. Use the total as your shopping figure, then distribute it by feel.

Bags are commonly sold in 100 g, 250 g, 500 g, and 1 kg sizes. Always round up to the nearest bag size. Leftover polyfill stores easily and keeps indefinitely in a sealed bag, so buying the next size up costs you nothing but shelf space, while running out mid-stuff means opening a seam you already closed.