How Much Weight Can a Deck Hold?
A 16 × 12 ft deck built to the IRC is designed for 40 psf of live load plus 10 psf of its own weight: 9,600 lb in all. Each interior post under the outer beam carries 2,400 lb and the ledger 300 lb per foot.
Design load by deck size, 40 psf live load, on a ledger with one beam:
| Deck | Design load | Busiest post | Ledger |
|---|---|---|---|
| 10 × 10 ft | 5,000 lb | 1,250 lb (2 posts) | 250 lb a ft |
| 12 × 12 ft | 7,200 lb | 1,800 lb (2 posts) | 300 lb a ft |
| 16 × 12 ft | 9,600 lb | 2,400 lb (3 posts) | 300 lb a ft |
| 16 × 16 ft | 12,800 lb | 3,200 lb (3 posts) | 400 lb a ft |
| 20 × 16 ft | 16,000 lb | 4,000 lb (3 posts) | 400 lb a ft |
The live load is a design number for people, furniture and grills spread across the deck, not a limit you can pile up to anywhere. The framing, ledger and footings are all sized for it, so a heavy load in one spot is what to check.
Can My Deck Hold a Hot Tub?
Not as built to the span tables. A filled hot tub puts its whole weight on a small footprint, and even a modest tub loads it at twice the design load or more:
| Hot tub | Filled, with people | Per sq ft |
|---|---|---|
| 250 gal, 6 × 6 ft | 2,935 lb | 82 psf |
| 350 gal, 7 × 7 ft | 4,319 lb | 88 psf |
| 400 gal, 7 × 7 ft | 4,836 lb | 99 psf |
| 500 gal, 8 × 8 ft | 6,120 lb | 96 psf |
Water at 8.34 pounds a gallon and 175 pounds a person; a tub's empty weight and gallons are on its spec sheet, or you can work out the gallons from its size. The pressure under a tub against what a deck is framed for:
The AWC's prescriptive deck guide leaves hot tubs out of its scope, so a tub on a deck needs framing designed for that load, with its own posts and footings under the footprint. On the ground, a tub can sit on a concrete slab instead.
How to Calculate Deck Load
Multiply the area by the live load plus the 10 psf dead load. Then split it: half the deck hangs on the ledger and half on the beam:
A post carries the deck between the beam and the middle of the joists, over half the distance to the next post on each side:
- 1Ledger: 300 lb per foot
- 2Beam: half the deck
- 3Inner post: 48 sq ft, 2,400 lb
The end posts carry half as much as the inner one. The post load is what sizes the footing: the IRC footing table for 48 sq ft on 1,500 psf soil gives an 18 in round footing. It bears on 1.77 sq ft, and at 1,500 psf the soil under it carries 2,651 lb, more than the post's 2,400 lb. The deck calculator sizes the footings, beam and ledger fasteners.
The ledger load is why the IRC lists lag screw and bolt spacing by joist span (R507.9). At 300 lb a foot, the 1/2 in lag screws go every 15 in on a 12 ft joist span.
Heavy Loads in One Spot
The test for anything heavy is the same as for a hot tub: its weight divided by the area it stands on, against 40 psf.
- Water: a cubic foot weighs 62.4 lb (7.48 gal × 8.34 lb), so water deeper than about 7 3/4 in is over 40 psf by itself. Cold plunges, stock-tank pools and big rain barrels all qualify.
- Planters: wet soil is heavy, and a planter box concentrates it; DCA 6 lists planters with hot tubs as loads outside its tables.
- Building materials: a pallet of pavers or a stack of bags on the deck during a project is a short-term load, but it is still a load in one spot. Spread it out or set it on the ground.
- Where the load sits: weight near the beam or over a post goes straight down; weight at the middle of the joists bends them most.
Deck Load Rules
- Live load: 40 psf for decks (IRC Table R301.5), or the ground snow load if greater (R507.1).
- Dead load: 10 psf in the IRC deck span tables, the weight of the framing and decking.
- Guards and stairs: a guard must resist 200 lb at its top, balusters 50 lb, and each stair tread a 300 lb point load (Table R301.5).
- Ledger: lag screws or bolts to the house band joist, never nails (R507.8).
- Beyond the tables: DCA 6 covers neither concentrated loads like hot tubs and planters nor snow loads over 40 psf.
Under a ground snow load of 50 to 70 psf, the same joists span less: check the joist span in the snow columns of the IRC table, or work out the snow load on a roof.
Frequently Asked Questions
How much weight can a deck hold?
A deck built to the IRC is designed for 40 pounds per square foot of live load, people and furniture, plus 10 psf for its own weight, or more where the ground snow load is higher. A 16 × 12 ft deck is designed for 7,680 pounds of live load, 9,600 in all.
How much weight can a deck hold per square foot?
40 pounds of live load per square foot, the IRC design load for decks (Table R301.5), on top of about 10 psf for the deck itself. In metric, 40 psf is about 195 kg per square meter.
Can my deck hold a hot tub?
Usually not without added framing. A 400 gallon tub weighing 800 pounds empty, with four people, puts about 98.7 pounds on each square foot of a 7 × 7 ft footprint, more than twice the 40 psf a standard deck is built for.
Can my deck hold 2,000 pounds?
Spread out, yes: 2,000 pounds over 50 square feet or more is no more than 40 psf. Set on a small footprint, the same weight can be several times the design load, which is why hot tubs, water tanks and stacked materials need a check.
Can a deck hold an inflatable hot tub or a pool?
Work it out the same way: water weighs 8.34 pounds a gallon, so 250 gallons is about 2,085 pounds before the people. Any water deeper than about 8 inches weighs more than 40 pounds per square foot, so a filled tub or pool is over the design load on its own.
How much weight does each deck post carry?
The deck area it supports times 50 psf. On a 16 × 12 ft deck with a ledger and three posts 8 ft apart, an interior post carries 6 × 8 = 48 square feet: 2,400 pounds.
How much does a gallon of water weigh?
8.34 pounds, so a 400 gallon hot tub holds 3,336 pounds of water.
What snow load does my deck need?
The IRC designs decks for the greater of 40 psf live load and the ground snow load where you build; its span tables run to 70 psf of snow.
Sources
- American Wood Council. (2018). Prescriptive residential wood deck construction guide: Based on the 2015 International Residential Code (DCA 6-15).
- International Code Council. (2020). 2021 International Residential Code (Table R301.5, Sections R507.1, R507.3, R507.9).
- U.S. Geological Survey. (2004). Estimated use of water in the United States in 2000: Conversion factors (Circular 1268).
Updated .
Cite this page as:
Daniel, P. Deck Load Calculator. Available at: https://constructioncalculators.com/deck-load-calculator/. Accessed: October 28, 2026.