Shelf span chart
The longest a shelf can span between supports before it sags past L/360, carrying 25 lb per running foot — about what a shelf of hardback books weighs. Sitting on supports rather than built in at both ends.
| Material | 1/2" thick | 3/4" thick | 1" thick |
|---|---|---|---|
| MDF | 18 3/16" | 27 1/4" | 36 5/16" |
| Melamine-faced particleboard | 16 7/8" | 25 5/16" | 33 3/4" |
| Particleboard | 16 7/8" | 25 5/16" | 33 3/4" |
| Baltic birch plywood | 26 3/4" | 40 3/16" | 53 9/16" |
| Hardwood plywood | 26 3/16" | 39 5/16" | 52 7/16" |
| OSB | 21 1/4" | 31 7/8" | 42 1/2" |
| Softwood plywood (CDX) | 25" | 37 1/2" | 50" |
| MDO plywood | 25 5/8" | 38 7/16" | 51 1/4" |
| Hardboard (Masonite) | 20 5/16" | 30 1/2" | 40 5/8" |
| Walnut (solid) | 27 3/16" | 40 13/16" | 54 7/16" |
| White oak (solid) | 27 3/4" | 41 5/8" | 55 1/2" |
| Red oak (solid) | 27 15/16" | 41 15/16" | 55 7/8" |
| Hard maple (solid) | 28" | 42" | 56" |
| Soft maple (solid) | 27" | 40 1/2" | 54" |
| Cherry (solid) | 26 1/8" | 39 1/4" | 52 5/16" |
| Poplar (solid) | 26 11/16" | 40" | 53 5/16" |
| Ash (solid) | 27 9/16" | 41 5/16" | 55 1/16" |
| Hickory (solid) | 29 5/8" | 44 3/8" | 59 3/16" |
| Mahogany (solid) | 26 3/16" | 39 5/16" | 52 7/16" |
| Sapele (solid) | 27 9/16" | 41 3/8" | 55 3/16" |
| White pine (solid) | 24 5/8" | 36 7/8" | 49 3/16" |
| Douglas fir (solid) | 28 5/8" | 42 7/8" | 57 3/16" |
| Cedar (solid) | 23 11/16" | 35 9/16" | 47 7/16" |
Reading it
- L/360 is the IRC's floor limit, borrowed here. It is not law about a bookshelf — a woodworker's rule of a thirty-second of an inch per foot is stricter and often the one that matters visually.
- Doubling the thickness cuts the sag to an eighth, which is why a thicker shelf beats a stiffer species nearly every time.
- Built-in at both ends deflects about a fifth as much as sitting on supports. An edge stiffener on the front does more than either.
- Panel stiffness varies by mill more than wood varies by tree, so treat the panel rows as nominal.
Sources: Wood Handbook: Wood as an Engineering Material (FPL-GTR-282, 2021), USDA Forest Service, Forest Products Laboratory; 2021 International Residential Code, International Code Council.
For the case this table does not cover
- Shelf sag and span
How far a shelf bends under books, how far it can span, and what a strip on the front edge buys you.
- Bookshelf spacing calculator
How many shelves fit a bookcase for the books going on it, even marks for each one, and whether the span will sag.
- Closet shelving
Shelf and rod heights for a single-hang, double-hang or shelf-only closet, with the shelf's sag checked.