calcs.homes
calcs.homes
Enter your deck's size to find the total design load it needs to support under standard residential code values.
Estimate only — actual framing capacity depends on joist size, spacing, and span. Have a professional verify.
Total design load multiplies deck area by the sum of live load (people and movable furniture) and dead load (the deck structure's own weight) per square foot. We default to 40 psf live load and 10 psf dead load — 50 psf total, the standard US residential minimum — and estimate occupancy by dividing live load capacity by 200 lb per person, rounding down to a whole number.
40 psf live load is a code floor, not a design target — it assumes typical furniture and foot traffic, so concentrated loads like a hot tub need engineered framing beyond this baseline. The 200 lb-per-person figure is a conservative planning average, not a hard limit, since actual safe capacity also depends on how evenly people are distributed and whether the deck was actually framed to carry the load it's rated for.
40 psf (pounds per square foot) is the standard US residential code minimum for typical decks — hot tubs and other concentrated loads usually need engineered framing beyond this baseline.
This calculator gives a rough capacity based on code live load and an average 200 lb per person — but actual safe occupancy also depends on how the load is distributed and whether the deck was built to code. A structural inspection is the only way to know for certain, especially on an older deck.