Three densities, three uses
- Product density: mass of the food per cubic metre of the food itself. Useful only for loose bulk materials and as an upper limit.
- Stack density: mass per cubic metre of the stack of cartons, crates, bottles or tubs, including packaging and the gaps between packs. This is what you need to size shelves and pallets.
- Gross room density: mass per cubic metre of the whole internal room volume, including aisles, wall gaps and headroom. It equals stack density × utilisation and is what a builder means by 'tonnes per room'.
Product densities that are well established
These are approximate values for the material itself, not for packed stock. They set a ceiling: no stack can be denser than the product inside it.
| Material | Approximate density | Note |
|---|---|---|
| Water | 1,000 kg/m³ | Most drinks and dairy liquids are close to this |
| Ice | about 917 kg/m³ | Ice is less dense than water |
| Milk | about 1,030 kg/m³ | Varies slightly with fat content |
| Butter, edible oils and fats | about 900 to 950 kg/m³ | Fats are lighter than water |
| Lean meat and fish | about 1,000 to 1,100 kg/m³ | Fattier cuts are lower |
| Ice cream | Mix density ÷ (1 + overrun) | With 100% overrun, roughly half the mix density |
Stack densities: calculate from your packs
Stack density depends on pack shape and how packs nest, so it is better calculated than quoted. Weigh a full pack, measure the space it occupies in a stack, and divide. The rows below are worked from assumed pack sizes and masses to show the range; replace them with your own measurements.
| Pack (assumed) | Mass | Space per pack | Stack density |
|---|---|---|---|
| 330 ml can, square grid, 66 × 66 × 115 mm cell | 0.35 kg | 0.50 L | about 700 kg/m³ |
| 1 L PET bottle, 85 × 85 × 300 mm cell | 1.03 kg | 2.17 L | about 475 kg/m³ |
| Frozen food carton 400 × 300 × 165 mm | 10 kg | 19.8 L | about 505 kg/m³ |
| 4 L ice-cream tub 245 × 170 × 115 mm, 100% overrun | 2.35 kg | 4.79 L | about 490 kg/m³ |
Gross room density: what the room really holds
Gross room density = stack density × utilisation, where utilisation is the share of internal volume occupied by stock. As a verified reference for a large bulk store, the National Horticulture Board's type design for potato storage holds 1,250 tonnes in a chamber of 21 × 16 × 13.7 m, which is about 270 kg per cubic metre of gross chamber volume for bagged potatoes.
Small walk-ins with shelving and a walkway are much less dense. With a stack density of 500 kg/m³ and utilisation of 0.35, a shelved chiller holds about 175 kg per cubic metre of room.
How to measure your own figure
- Pick the three or four pack types that make up most of your stock.
- Weigh one full pack of each on a kitchen or platform scale.
- Measure the space each occupies in a stack, including any unavoidable gap, such as round bottles in a square grid.
- Divide mass by volume for each, then weight the average by how much of each you hold.
- Check against a real shelf: load one, weigh what it holds and compare with your estimate.
Using density in sizing
To size a room or cabinet: volume of stock (m³) = mass (kg) ÷ stack density (kg/m³), then room volume = stock volume ÷ utilisation. To check an existing room: mass it can hold = room volume × utilisation × stack density. Keep the three densities labelled in your working, and the estimate stays honest.
Frequently asked questions
- Why is my packed stock so much lighter per cubic metre than water?
- Because packaging, air inside packs (as in ice cream), and gaps between round or irregular packs take up space. Even drinks, which are nearly as dense as water, stack at well under 1,000 kg/m³ once bottles and gaps are counted.
- Is there a single kg per m³ figure for a cold room?
- No. It depends on the product, the packs and the layout. Use the NHB potato figure only as a reference point for large bulk stores; small walk-ins with mixed stock and shelving hold far less per cubic metre.