Shelf Weight Capacity Calculator
Calculate the maximum weight a shelf can hold based on material, length, depth, and support spacing.
Avoid overloaded shelves.
How Shelf Weight Capacity Is Calculated
Shelf load capacity depends on material, thickness, span between supports, and mounting method. Exceeding capacity causes sagging, joint failure, or collapse.
Distributed Load Formula:
Max Load (kg) = (Material Strength × Thickness³ × Width) / (Support Span² × Safety Factor)
In practice, use published tabular data for common shelf materials. The span-to-thickness ratio is the most useful field rule:
Safe Span-to-Thickness Rules (for books/heavy loads):
- Solid wood (hardwood): max span = 24 × thickness
- Plywood (3/4 inch / 19mm): max span = 900mm before sagging
- MDF (19mm): max span = 750mm (MDF sags more than plywood)
- Glass (10mm tempered): max span = 600mm at 20 kg/m load
Worked Example: 19mm plywood shelf, 900mm wide, spanning 800mm between supports, loaded with books:
- Span limit ≈ 900mm — at 800mm, marginally safe but will sag under heavy books
- Recommendation: add a center support or use 25mm plywood for this span
Capacity Estimates (distributed load, safe working):
| Material & Thickness | 600mm Span | 900mm Span | 1200mm Span |
|---|---|---|---|
| 19mm plywood | 40 kg | 25 kg | 12 kg |
| 25mm hardwood | 65 kg | 40 kg | 20 kg |
| 19mm MDF | 30 kg | 18 kg | 8 kg |
Mounting Matters: Wall brackets into studs hold 50–100 kg each. Drywall anchors alone: 10–20 kg maximum.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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