Shelf Sag Calculator

Nothing ruins the look of a bookcase or built-in faster than sagging shelves. This calculator helps you design shelves that will remain straight under load for years to come.

Simply enter your shelf dimensions, material, and expected load to see how much deflection to expect. The calculator will tell you if your design passes the generally accepted limit of 1/360 of the span.

Use this tool when planning:

Bookcases and media centers
Kitchen and pantry shelving
Closet organization systems
Workshop storage

Understanding Shelf Deflection

Shelf sag is calculated using beam deflection formulas from engineering mechanics. The key factors are the material's modulus of elasticity (stiffness), the shelf's cross-sectional dimensions, the span length, and the applied load.

Tips for reducing sag: Increase thickness, reduce span with center supports, use stiffer materials like plywood or hardwoods, or add a face frame to increase effective depth.