Shelf Span & Sag Calculator
Check whether a shelf will hold — and how far apart the brackets can go — before you drill anything.
1137mmmax span between supports
- Verdict
- Comfortable
- Supports needed
- 2
- Spacing
- 800 mm apart
- Sag at this span
- 1.5 mm
How this works: standard beam-deflection maths for a uniformly loaded shelf on two supports, held to the L/180 limit — the point at which sag becomes noticeable to the eye. Thickness dominates because stiffness scales with thickness cubed, while depth only scales linearly.
Assumes the load is spread evenly and the supports are solid — fixed into studs or masonry, not just plasterboard. A heavy object in the middle of the span deflects considerably more than the same weight spread out. Glass should always be toughened and edge-polished.