Deck Footing Calculator
* Does not include excavation, rebar, post brackets, or labor. Assumes 6 ft post spacing and IRC 2021 requirements. Check local frost depth.
Disclaimer: Estimates are for budgeting purposes only. Actual costs vary by location, contractor, material availability, and project complexity. Always get professional quotes for exact pricing.
Deck Footing Concrete Requirements
| Footing Size | Concrete / Footing | 60 lb Bags |
|---|---|---|
| 12" × 48" | 3.1 cu ft | 7 bags |
| 16" × 48" | 5.6 cu ft | 12 bags |
| 18" × 48" | 7.1 cu ft | 16 bags |
| 12" × 60" | 3.9 cu ft | 9 bags |
Footings Needed by Deck Size
| Deck Size | Footings | Concrete (16" footings) |
|---|---|---|
| 12×10 | 8 footings | 45 cu ft (1.7 cu yd) |
| 16×12 | 10 footings | 56 cu ft (2.1 cu yd) |
| 20×16 | 14 footings | 78 cu ft (2.9 cu yd) |
| 24×20 | 18 footings | 101 cu ft (3.7 cu yd) |
* Assumes 6 ft post spacing. Add footings for interior beams on large decks.
How We Calculate
Our deck footing calculator estimates footings needed based on deck dimensions and footing size. Calculations follow IRC 2021 guidelines for post spacing and bearing loads.
How the math works: Perimeter footings = (2 × length + 2 × width) ÷ 6 ft spacing. Interior footings added for large decks. Concrete volume = footings × (π × radius² × depth). Convert to bags or cubic yards based on total volume.
Footing Size Selection
12" diameter × 48" deep (3.1 cu ft, 7 bags) is minimum for decks under 200 sq ft. Use for simple ground-level decks with light loads. Adequate for 4×4 posts and 2×6 beams.
16" diameter × 48" deep (5.6 cu ft, 12 bags) is standard for most residential decks (200–400 sq ft). Supports 6×6 posts and double 2×8 beams. Required by some jurisdictions.
18" diameter × 48" deep (7.1 cu ft, 16 bags) for large elevated decks (400+ sq ft), decks with hot tubs, or poor soil. Provides maximum bearing capacity.
12" diameter × 60" deep (3.9 cu ft, 9 bags) for deep frost lines (northern climates). Same diameter as standard but extends to 60" depth for frost protection.
Bags vs Ready-Mix
60 lb bags ($5 each, covers 0.45 cu ft) are cost-effective for small projects (under 1 cu yard = 60 bags). Mix in wheelbarrow or portable mixer. Allows you to work at your own pace. Exhausting to mix by hand for large jobs.
Ready-mix delivery ($125–$175/cu yard + $100 delivery) is better for large projects (over 1 cu yard). Minimum order usually 1 yard. Must pour all footings same day. Professional finish, less labor. Calculate 10–15% overage for waste.
Additional Costs
Our estimates cover concrete only. Not included: excavation/auger rental ($75/day or $3–$5/ft professional), sonotube forms ($8–$15 per 4 ft tube), rebar ($3–$5 per footing), post brackets ($8–$15 each), gravel base ($30–$50 for 6" layer), and inspection fees ($50–$150).
Data Sources
Footing requirements per IRC 2021. Concrete volumes calculated using π × r² × h formula. Pricing from Home Depot, Lowe's, and ready-mix suppliers. We review and update regularly.
Last updated: 2026-02-09
Frequently Asked Questions
How many footings do I need for a deck? +
Deck footings are spaced 6–8 ft apart around the perimeter. Formula: (perimeter ÷ 6 ft) + interior footings. A 16×12 deck has 56 ft perimeter ÷ 6 = 10 footings. Large decks (16+ ft) need interior footings every 8 ft for beam support. Corners always get footings. Check local codes for spacing requirements.
What size footing do I need for a deck? +
Standard deck footings: 12" diameter × 48" deep for small decks (under 200 sq ft), 16" × 48" for medium decks (200–400 sq ft), 18" × 48" for large decks (400+ sq ft). Frost line determines depth — dig 6" below frost line (48–60" in northern states, 12–24" in southern states). Use sonotube forms for easy pouring.
How much concrete do I need for deck footings? +
12" diameter × 48" deep footing holds 3.1 cu ft (0.11 cu yards). One 60 lb bag covers 0.45 cu ft, so 7 bags per footing. 16" × 48" footing holds 5.6 cu ft (12 bags). Order ready-mix if you need more than 1 cu yard (27 cu ft). For 10 footings at 16": 56 cu ft = 2.1 cu yards.
Can I pour deck footings myself? +
Yes, DIY deck footings are straightforward. Rent auger for digging ($75/day). Use sonotube forms ($8–$15 per 4 ft tube). Mix 60 lb bags in wheelbarrow or mixer. Pour concrete, level top, insert post bracket while wet. Allow 3–7 days to cure before building. Professional auger/pour costs $50–$100 per footing if you prefer.
Do deck footings need rebar? +
Rebar is not required for most residential deck footings per IRC but is recommended. Add 2–3 pieces of #4 rebar (1/2") vertically in each footing for strength. Costs $3–$5 per footing. Required for: large decks (over 500 sq ft), decks with hot tubs, seismic zones, and expansive soils. Check local building codes.
What is frost depth and why does it matter? +
Frost depth is how deep soil freezes in winter. Footings must extend 6" below frost line to prevent frost heave (soil expansion that lifts posts). Frost depths: northern states 48–60", Midwest 36–48", mid-Atlantic 24–36", southern states 12–24". Call local building department for exact depth. Shallow footings can crack your deck frame.
How far apart should deck posts be? +
Deck posts are spaced 6–8 ft apart for typical beam spans. 6 ft spacing for 2×8 beams, 8 ft for 2×10 or double 2×8 beams. Posts must be at every corner and along perimeter at spacing intervals. Interior posts support mid-span beams. Maximum cantilever beyond last post: 1/4 of beam span (2 ft for 8 ft spacing).
Do I need a permit for deck footings? +
Yes, most jurisdictions require permits for deck construction including footings. Building inspector verifies footing depth, diameter, and spacing meet code. Permit costs $100–$500 depending on deck size. Inspection happens before pouring concrete and after framing. Unpermitted decks can force removal during home sale and void homeowner insurance for accidents.
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