Sizu Riatto
Flush Hour · Chapter 4

Box Math

Measure the tub once and you know how much straw fills it before you buy a bale. Volume, depth and the area of every hole, from a tape measure and one density.

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Opens on the book's tub. Change any number to your own and press Calculate.

Inside measurements (measure inside: totes taper)

The straw

The holes

Enter the inside measurements, then press Calculate.

The formula

  • Box: volume = length × width × depth; 1,000 cm³ = 1 L. Round bucket: floor = π × (diameter ÷ 2)², volume = floor × depth
  • Straw volume (L) = dry straw (kg) ÷ packed density (kg a m³) × 1,000
  • Fill depth = straw volume (cm³) ÷ floor area (cm²); percent full = straw volume ÷ tub volume × 100
  • Dry straw to a fill line = floor × depth ÷ 1,000 (L) × density ÷ 1,000
  • A circle's area = π × r², with r = diameter ÷ 2; total hole area = holes × one hole
The book's worked example, Chapter 4. The book's tote measures 55 × 36 × 28 cm inside: 55.44 L on a 1,980 cm² floor. Packed straw holds about 40 kg of dry matter a m³, so 1.80 kg takes 45 L, 22.73 cm deep, 81.17% full. Ten holes of 25 mm (0.98 in) make 49.09 cm².
Check it. Call the dry straw that fills your tub to its line, then weigh it in flake by flake.

Honest limits. The density is an estimate between loose and tapped straw in one lab's test (36 and 43 kg a m³): chopping, packing and the straw itself move it, so weigh your own. A tote's sides taper, so its label's liters are not its inside volume. The book's tub, its straw and its harvests were worked out on paper from published figures, not grown by us: weigh your own. Prices are illustrative, as seen in November 2026 (US mid prices, with UK beside where they differ), shown without a currency sign; put in your own. No yield or profit is promised. Everything stays in your browser: no sign-up, nothing stored.