How far can a shelf span before it visibly sags? The table below is computed — not copied — from each species' USDA modulus of elasticity, using published beam formulas, long-term creep included, floating ends, load spread evenly. The limit is the 0.02 in/ft visibility standard from our sag guide.
| Species (3/4 in thick, 11 in deep) | 15 lb/ft | 25 lb/ft | 35 lb/ft |
|---|---|---|---|
| White Oak | 36 in | 30 in | 27 in |
| Red Oak (Northern) | 36 in | 30 in | 27 in |
| Hard Maple (Sugar Maple) | 36 in | 30 in | 27 in |
| White Ash | 35 in | 30 in | 27 in |
| Black Walnut | 35 in | 29 in | 26 in |
| Black Cherry | 34 in | 28 in | 25 in |
| Yellow Poplar | 34 in | 29 in | 26 in |
| Douglas Fir (Coast) | 37 in | 31 in | 28 in |
| Eastern White Pine | 31 in | 26 in | 24 in |
| Red Maple | 35 in | 29 in | 26 in |
Read it as a ceiling, not a target: spans assume clear, straight-grained stock at furniture moisture. Knots, grain runout and a toddler using the shelf as a ladder all argue for margin. Fixed ends (glued dados) buy roughly 25–40% more span; a 1½″ front edging strip buys more again — the calculator combines them properly. Sheet goods live in a different world: fir plywood spans like a mid-pack hardwood, while MDF and particleboard at 25 lb/ft belong under about two feet of span at this thickness.
Every species page carries its own span table, including 1″-thick shelves: start from the species index.