Deck Foundation Calculator

The Deck Foundation Calculator sizes the concrete footings and posts needed to safely support an outdoor deck based on its dimensions and structural loads. Enter your deck length, deck width, joist length, post spacing, dead load, live load, soil bearing capacity, and whether the deck is attached to the house or freestanding. You'll get the corner footing diameter, intermediate footing diameter, total posts required, number of beams, maximum load per post, and total deck load.

ft
ft
psf

Weight of deck materials (typical: 10 psf)

psf

Occupancy and furniture load (typical: 40 psf)

psf

Consult local building codes or engineer

Deck Attachment *

Results

Corner Footing Diameter

--

Intermediate Footing Diameter

--

Total Posts Required

--

Number of Beams

--

Maximum Load per Post

--

Total Deck Load

--

More Construction Tools

Frequently Asked Questions

How many deck blocks or footings do I need?

The number of footings depends on your deck size, post spacing, and load requirements. Generally, you'll need corner footings plus intermediate footings based on your beam layout and post spacing.

What size footing do I need for my deck?

Footing diameter depends on the load per post and soil bearing capacity. Corner posts typically carry more load and may require larger footings than intermediate posts.

How far apart should deck posts be spaced?

Post spacing typically ranges from 4-8 feet, with 6-7 feet being most common. Closer spacing reduces beam size requirements but increases the number of footings needed.

What is the difference between dead load and live load?

Dead load is the weight of the deck structure itself (joists, beams, decking), typically 10 psf. Live load accounts for people, furniture, and temporary loads, typically 40 psf for residential decks.

Should my deck be attached to the house or freestanding?

Attached decks use a ledger board connected to the house, reducing the number of footings needed. Freestanding decks require additional support but don't affect the house structure.

How do I determine my soil bearing capacity?

Soil bearing capacity varies by soil type and should be determined by local building codes or a geotechnical engineer. Typical values range from 1,500-3,000 psf for most residential applications.

Can I use concrete deck blocks instead of poured footings?

Pre-cast concrete blocks work for smaller, ground-level decks with lighter loads. For elevated decks or higher loads, poured concrete footings extending below the frost line are typically required.