Scaffolding Load Calculator — OSHA Duty Ratings

Short answerOSHA duty ratings are load per square foot: light 25 psf, medium 50 psf, heavy 75 psf. Capacity = platform area × duty rating; every scaffold must also support 4× the maximum intended load.

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How it's calculated

OSHA classifies scaffolds by uniform load: light-duty for inspection and light work, medium-duty for most trades, heavy-duty for masonry and stockpiling. Multiply the platform area by the rating to get capacity, keep the intended load below it, and confirm the 4:1 safety factor on the structure.

Capacity(lb) = Area(ft²) × Duty(psf) Structure safety factor ≥ 4 × max intended load

Worked example

Platform 7 × 5 = 35 ft², heavy duty (75 psf).
Capacity = 35 × 75 = 2,625 lb.

Reference tables

OSHA scaffold duty ratings

Duty	Uniform load	Use
Light	25 psf	inspection, light work
Medium	50 psf	most trades
Heavy	75 psf	masonry, stockpiling

A number the tables do not give: a 35 ft² heavy-duty platform is rated for about 2,625 lb of uniform load at 75 psf.

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FAQ

What does the duty rating mean?

It is the maximum uniform load per square foot the platform is designed for; pick the class that matches the work.

What is the 4:1 rule?

Scaffolds and their components must be capable of supporting four times the maximum intended load without failure.

Do point loads change it?

Yes — concentrated loads (a stack of block) can exceed the uniform rating locally; distribute loads or use planking rated for them.

Does this replace an engineer?

For non-standard or high scaffolds, OSHA requires design by a qualified person. Treat this as a duty-rating check only.

This page is a reference aid. Always verify against OSHA 1926 Subpart L and the scaffold manufacturer data. Figures shown are for orientation, not a stamped design.

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