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Shelf Load Capacity Calculator

Work out shelf load capacity instantly with clear inputs, formula shown and shareable results.

About Shelf Load Capacity Calculator

Shelf capacity is governed by deflection, not strength: a shelf that sags 10 mm looks broken long before it fails. Deflection scales with span cubed and inversely with thickness cubed, so halving the span multiplies capacity eightfold — far more effective than a thicker board.

Formula

Shelf deflection

allowable load = (span/200) x 384 E I / (5 x span^3), with I = depth x thickness^3 / 12

Worked example

With the default values below, Shelf Load Capacity Calculator returns Safe distributed load of 24.67. Change any input above and every figure here is recalculated in your browser.

Inputs used

Shelf span
900 mm
Shelf thickness
18 mm
Shelf depth
300 mm
Materialone of Solid hardwood, Plywood, MDF, Chipboard / melamine
MDF

Results

Safe distributed load
24.67 kg
Deflection at that load
4.50 mm
Load per metre of shelf
27.41 kg/m
Assessment
Suitable for books at short spans

Step by step

  1. 1Values used
  2. 2Shelf deflection
  3. 3Safe distributed load= 24.67 kg
  4. 4Deflection at that load= 4.50 mm
  5. 5Load per metre of shelf= 27.41 kg/m
  6. 6Assessment= Suitable for books at short spans

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why limit deflection to span over 200?

It is the point at which sag becomes visually obvious. Structural failure happens much later, but nobody accepts a visibly bowed shelf.

What is the cheapest way to increase capacity?

A centre support. Halving the span increases capacity by eight times, whereas doubling thickness only achieves the same eight times at far greater cost and weight.

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