Find how far apart to place shelf supports so the shelf does not sag. Pick the material, thickness, load, and shelf width.
Max Span Between Supports
— in.
Keep brackets within this spacing.Usage Tip
A 1×2 stiffener glued and screwed under the front edge of a shelf can roughly double its usable span. For heavy garage loads, support every 16 in over a stud.
THE MATH
Allowable span depends on material stiffness, thickness, and load
Thicker shelves and stiffer woods span farther
Supports needed = round up (width ÷ max span) + 1
Thicker shelves and stiffer woods span farther
Supports needed = round up (width ÷ max span) + 1
Shelves sag under load over time (creep), especially particleboard and MDF. The fix is closer supports, a thicker shelf, a stiffer material, or a front-edge stiffener.
These spans target a barely visible sag for typical loads; they are guidelines, not tested weight ratings.
These spans target a barely visible sag for typical loads; they are guidelines, not tested weight ratings.
Particleboard and MDF sag the most and keep sagging under sustained load; solid hardwood and plywood hold much better.
A wood strip glued under the front edge dramatically stiffens a shelf and can roughly double the span.
For heavy, concentrated loads (a single toolbox, an aquarium, tightly packed books), add supports and do not rely on span charts — check the bracket and material ratings.
A wood strip glued under the front edge dramatically stiffens a shelf and can roughly double the span.
For heavy, concentrated loads (a single toolbox, an aquarium, tightly packed books), add supports and do not rely on span charts — check the bracket and material ratings.