Calculate the number of joists, hangers, and blocking needed for floors and ceilings.
Enter the room length (the direction joists are spaced along) and the room width (the span the joists cross), then choose the joist spacing. The tool returns the joist count plus the hangers, blocking (“noggins” in the UK) and rim joists you will need.
| Spacing | Use |
|---|---|
| 16 in / 400 mm | Standard floors |
| 19.2 in / 488 mm | Engineered joists |
| 24 in / 600 mm | Lighter loads, thicker decking |
A room 5 m long with joists at 400 mm centres needs 5000 ÷ 400 + 1 = 14 joists. Each spans the 4 m width, so you need 14 joist hangers each end and a row of blocking across the middle to stop the joists twisting.
Tip: joists should span the shorter dimension of the room, and the depth needed grows with the span — always confirm the size against a span table or building code before buying.
16 inches (400 mm) on center is standard for residential floors. 12 inches may be needed for heavier loads like tile floors.
It depends on the joist size and wood species. A 2×10 SPF joist at 16" spacing can typically span around 15 feet for a 40 psf live load.
Yes, bridging or blocking is required at mid-span (or every 8 ft) for stability and to prevent joist twisting under load.
Domestic floors are usually designed for about 1.5 kN/m² (around 30 lb/ft²) of live load plus the floor’s own weight. The safe load depends on joist size, spacing and span — check span tables.
Joists normally span the shortest distance between supporting walls or beams, running at right angles to the floorboards above. Keeping the span short helps stiffen the floor.
