Bookshelf Design Calculator

Calculate shelf deflection, maximum safe span, minimum thickness, and material requirements based on load, wood species, and dimensions.

Shelf span (in)

Shelf depth (in)

Shelf thickness (in)

Load per foot (lbs/ft)

Number of shelves

Wood (0=Pine..3=Maple,5=Ply,6=MDF)

Shelf spacing (in)

Tab to move between fields

Predicted center sag (in)

0.07

Sag ratio (< 1 = OK)

0.4

Max acceptable sag (in)0.18

Max safe span (in)48.9

Min thickness for this span (in)0.55

Board feet per shelf2.11

Total board feet (all shelves)10.55

Estimated bookcase height (in)64.5

Total weight capacity (lbs)375

Wood NameRed Oak

Passes DeflectionYes

How to Use This Calculator

Enter the Shelf Span (unsupported distance) in inches and Shelf Depth for your bookcase design.
Enter the Shelf Thickness, Load Per Foot in lbs/ft (books average 20–30), and Number of Shelves.
Select the Wood Type to apply the correct modulus of elasticity for deflection calculations.
Review Predicted Center Sag and Sag Ratio — keep it below 1.0 for safe, sag-free shelves.
Check Max Safe Span and Min Thickness for your load to confirm or upgrade your material choice.

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