WoodCalcs.uk
Bed Frame Calculator — Dimensions & Slat Spacing
Calculate bed frame dimensions, slat spacing, and timber quantities for UK standard mattress sizes.
How We Calculate This
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 width + Max gap))
Slats are laid flat across the frame, so each slat's footprint along the bed length is its width (typically 70mm), not its thickness. 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.
Frequently Asked Questions
UK standard sizes are: Single 90x190cm, Small Double 120x190cm, Double 135x190cm, King 150x200cm, Super King 180x200cm. Note that UK sizes differ from EU and US sizes. Always measure your actual mattress before building.
Most UK mattress warranties require slat gaps of no more than 70mm (some specify 60mm). For memory foam mattresses, closer spacing (30-50mm) is recommended for better support. This calculator automatically determines the number of slats to keep gaps within 70mm.
A centre support rail is strongly recommended for any bed wider than 1400mm (king size and above). It prevents slats from bowing under body weight and significantly increases the rigidity of the frame. Double beds (1350mm) can manage without but benefit from one.
Side rails and head/foot boards should be hardwood (oak, ash, beech) or quality softwood (redwood pine) at least 22mm thick and 150-200mm wide. Slats can be thinner (18mm) but should be at least 70mm wide. Use straight-grained stock without large knots for rails.
Allow 10mm clearance on each side and each end between the mattress and the frame interior. This makes it easy to fit sheets and prevents the mattress from being squeezed, which can damage it and void the warranty.
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Last updated: February 2026
All calculations are estimates. Always verify measurements and material quantities before cutting or purchasing.