Bed Frame Calculator — Dimensions & Slat Spacing

This calculator sizes a bed frame around UK standard mattress dimensions with proper clearances and slat spacing.

Frame sizing

Internal dimensions = Mattress size + 20mm (10mm clearance each side)

External dimensions = Internal + (2 x rail thickness)

Slat calculation

Number of slats = ceil((Frame length + Max gap) / (Slat thickness + Max gap))

With a slat at each end there are n − 1 gaps, so the slat count is rounded up to guarantee the actual gap never exceeds the 70mm maximum set by UK mattress warranties. Actual spacing is then calculated from the chosen count to distribute the slats evenly. Beds wider than 1400mm automatically include a centre support rail; slats span from each side rail to the centre rail, so the half-slat length subtracts the centre-rail width before halving the clear internal width.

Slat length is the clear internal frame width. In practice each slat rests on a ledger (cleat) fixed to the inside face of the side rails; if your slats instead sit on top of the rails, add a small bearing allowance to the cut length.