Calculator
Shelf Sag Calculator
Estimates deflection for a shelf resting on two supports with an evenly spread load. Under 0.02″ per foot of span is invisible to the eye.
Typical: books ≈ 20–25 lb/ft (30–37 kg/m), dishes ≈ 15 lb/ft, decor ≈ 5 lb/ft.
Shelf sag estimate
- Sag at center
- 0.071″
- Sag per foot of span
- 0.0237″
- Total load
- 75 lb
- Verdict
- Visible sag — go thicker, shorter or add a front edge
Wood also creeps over time: a shelf loaded for years can sag up to 1.5–2× this figure. A hardwood edge strip on the front stiffens a shelf dramatically.
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Build it · Intermediate · 1 day
Download the complete plan with cut list and materials list (PDF)
No-Sag Floating Shelves — Hollow-core floating shelves on a hidden 2×4 cleat—stiff enough for books. Drawings, cut list with board-foot totals, hardware list and step-by-step instructions.