The two-step method
Step 1, product volume: V_product (m³) = stored mass (kg) ÷ stack density (kg/m³). Stack density is the mass of product per cubic metre of the stack it forms, including its packaging and the gaps between cartons or crates, not the density of the food itself.
Step 2, room volume: V_room (m³) = V_product ÷ utilisation. Utilisation is the fraction of the internal room volume actually occupied by product once you allow for aisles, gaps from walls, clearance under the ceiling and evaporator, and empty shelf space. It is always well below 1.
Getting the stack density right
The most reliable figure is your own. Weigh a full carton, crate or tray and measure its outside dimensions: density = mass ÷ (length × width × height). A 12 kg carton measuring 0.40 × 0.30 × 0.20 m occupies 0.024 m³, so its stack density is 500 kg/m³.
As a reference point from a large bulk store, India's National Horticulture Board type design for potato storage puts 1,250 tonnes of bagged potatoes in a chamber of 21 × 16 × 13.7 m. That works out to roughly 270 kg per cubic metre of gross chamber volume. Small walk-ins with shelving and mixed product reach far less than that.
Utilisation: how much of the room the product fills
Utilisation depends mainly on the storage method and room size. The values below are planning assumptions used for a first estimate, not standards. Your builder's layout drawing replaces them.
| Storage method | Assumed utilisation | Why |
|---|---|---|
| Shelving on two walls, central walkway, small room | 0.30 to 0.40 | The walkway and shelf gaps take most of the volume |
| Shelving on three walls, larger room | 0.35 to 0.45 | Walkway shrinks relative to shelf length |
| Pallets in rows with a hand-pallet-truck aisle | 0.40 to 0.55 | Dense blocks, but the aisle and top clearance remain |
| Bulk bags or stacked cartons, no daily picking | 0.55 to 0.70 | Little aisle space, used for long-hold storage |
Worked example: a 1,500 kg chilled room
Assumptions: a hotel needs to hold 1,500 kg of mixed chilled product at +2 to +4 °C, mostly in crates and cartons; measured stack density averages 350 kg/m³; storage is on shelving along two walls with a central walkway, utilisation 0.35; internal height 2.4 m.
Product volume = 1,500 ÷ 350 = 4.29 m³. Room volume = 4.29 ÷ 0.35 = 12.2 m³. Floor area = 12.2 ÷ 2.4 = 5.1 m², for example 2.4 m long × 2.2 m wide inside.
Cross-check with a layout: two runs of shelving 0.6 m deep plus a 1.0 m walkway gives 2.2 m width. Two runs 2.4 m long × 0.6 m deep × 5 tiers = 14.4 m² of shelf. If product sits about 0.3 m high on each tier, that holds 14.4 × 0.3 = 4.3 m³, which matches step 1. The estimate is consistent.
From internal size to the footprint you need
The figures above are internal. Add the insulated panel thickness on every side and on top. Chiller panels are commonly in the 60 to 100 mm range and freezer panels thicker, often 100 to 150 mm; confirm with the builder. In the example, 100 mm panels make the outside about 2.6 × 2.4 m and the height about 2.6 m plus any floor insulation, before you add space for the condensing unit, door swing and service access.
Checks before you fix the size
- Peak, not average: size for the largest stock you hold, such as before a festival or a wedding season, plus deliveries that arrive before old stock is used.
- Separate temperatures: if some product needs a freezer, it needs a separate room or a freezer cabinet. One room cannot hold two temperature bands.
- Separation of raw and ready-to-eat food takes shelf space; do not plan at 100% shelf fill.
- Airflow: keep product clear of the evaporator face and below its discharge so cold air can travel the length of the room.
- Heat load comes next: room size sets the transmission and infiltration load, and the daily intake sets the product load.
Frequently asked questions
- Can I just use a kg per cubic metre figure for the whole room?
- You can for a quick check, but it hides the two separate effects: how densely your product packs and how much of the room the layout leaves for it. Splitting them makes it obvious when, for example, a wider aisle is costing you a lot of capacity.
- Is a bigger cold room always safer?
- No. An oversized room costs more to build and to cool, because transmission load grows with surface area. Size for real peak stock with a sensible margin, and leave space outside the room to extend it later if growth is likely.