FootingPad Size Chart - Tributary Area
Tributary area is the square footage of the deck surface area carried by one post. This can vary for each post based on configuration of the deck. This chart is comparable to chart R507 found in the International Residential Code (IRC) 2018 and beyond. Use 40 lbs per square foot snow load for any snow load up to 40 lbs.
Learn more about calculating the tributary area at:
 https://footingpad.com/decks-footing-size-calculation-guide
| Snow Load | Tributary Area | FootingPad Diameter by Soil Capacity (psf) | |||
|---|---|---|---|---|---|
| 1,500 psf | 2,000 psf | 2,500 psf | 3,000 psf | ||
| 40 psf | 20 sq. ft. | 10" Dia. | 10" Dia. | 10" Dia. | 10" Dia. |
| 40 sq. ft. | 16" Dia. | 16" Dia. | 12" Dia. | 10" Dia. | |
| 60 sq. ft. | 20" Dia. | 16" Dia. | 16" Dia. | 16" Dia. | |
| 80 sq. ft. | 24" Dia. | 20" Dia. | 16" Dia. | 16" Dia. | |
| 100 sq. ft. | 24" Dia. | 20" Dia. | 20" Dia. | 16" Dia. | |
| 120 sq. ft. | n/a | 24" Dia. | 20" Dia. | 20" Dia. | |
| 140 sq. ft. | n/a | 24" Dia. | 24" Dia. | 20" Dia. | |
| 160 sq. ft. | n/a | n/a | 24" Dia. | 20" Dia. | |
| 50 psf | 20 sq. ft. | 12" Dia. | 10" Dia. | 10" Dia. | 10" Dia. |
| 40 sq. ft. | 20" Dia. | 16" Dia. | 16" Dia. | 12" Dia. | |
| 60 sq. ft. | 24" Dia. | 20" Dia. | 16" Dia. | 16" Dia. | |
| 80 sq. ft. | 24" Dia. | 20" Dia. | 20" Dia. | 16" Dia. | |
| 100 sq. ft. | n/a | 24" Dia. | 20" Dia. | 20" Dia. | |
| 120 sq. ft. | n/a | 24" Dia. | 24" Dia. | 20" Dia. | |
| 140 sq. ft. | n/a | n/a | 24" Dia. | 24" Dia. | |
| 160 sq. ft. | n/a | n/a | n/a | 24" Dia. | |
| 60 psf | 20 sq. ft. | 16" Dia. | 12" Dia. | 10" Dia. | 10" Dia. |
| 40 sq. ft. | 20" Dia. | 16" Dia. | 16" Dia. | 16" Dia. | |
| 60 sq. ft. | 24" Dia. | 20" Dia. | 20" Dia. | 16" Dia. | |
| 80 sq. ft. | n/a | 24" Dia. | 20" Dia. | 20" Dia. | |
| 100 sq. ft. | n/a | 24" Dia. | 24" Dia. | 20" Dia. | |
| 120 sq. ft. | n/a | n/a | 24" Dia. | 24" Dia. | |
| 140 sq. ft. | n/a | n/a | n/a | 24" Dia. | |
| 160 sq. ft. | n/a | n/a | n/a | n/a | |
| 70 psf | 20 sq. ft. | 16" Dia. | 12" Dia. | 12" Dia. | 10" Dia. |
| 40 sq. ft. | 24" Dia. | 20" Dia. | 16" Dia. | 16" Dia. | |
| 60 sq. ft. | 24" Dia. | 24" Dia. | 20" Dia. | 20" Dia. | |
| 80 sq. ft. | n/a | 24" Dia. | 24" Dia. | 20" Dia. | |
| 100 sq. ft. | n/a | n/a | 24" Dia. | 24" Dia. | |
| 120 sq. ft. | n/a | n/a | n/a | 24" Dia. | |
| 140 sq. ft. | n/a | n/a | n/a | n/a | |
| 160 sq. ft. | n/a | n/a | n/a | n/a | |