Decking Calculators
Plan your deck project with calculators for footings, post spacing, joist spans, and total material estimates.
1 calculator available
Frequently Asked Questions
Footing spacing depends on your beam span. With doubled 2×10 beams, typical spacing is 8–10 feet. Verify against span tables in your local building code.
Footings must extend below the frost line: 12–18 inches in the deep South, 36–42 inches in the northern US, up to 60 inches in Minnesota. Check your local frost depth.
Most jurisdictions require a permit for decks over 200 sq ft or attached to the house. Always check local code before starting.
A 12-inch diameter sonotube holds about 0.785 cubic feet per linear foot. At 42 inches deep that is 0.327 cubic feet — roughly half an 80 lb bag per footing.
Yes — Quikrete Fast-Setting can be poured dry and watered in. It reaches 50 psi in 20–40 minutes, which works well for post holes.
A well-planned deck starts with accurate footing and material estimates. Undersized footings cause settlement; undersized material orders cause work stoppages. Our deck calculators help you get both right before the first shovel hits the ground.
Deck Calculator Tools
Enter post count, load area, and soil bearing capacity to get footing diameter and concrete volume per footing. Outputs total cubic feet and bag count for all footings.
Open calculator → Concrete Bags CalculatorQuick bag count for all your deck footings. Works alongside the footing calculator to give you a final order quantity.
Open calculator → Lumber CalculatorJoist, beam, and decking board quantities for any deck footprint.
Open calculator → Board Foot CalculatorFor pricing pressure-treated lumber orders by volume.
Open calculator →- Footings must extend below the frost line in your climate zone
- Northern US (Zone 5–7): 36–42 inches minimum depth
- Southern US (Zone 8–9): 12–18 inches is typically sufficient
- Always verify frost depth requirements with your local building department
Post Sizing by Deck Height
| Deck Height | Recommended Post Size |
|---|---|
| Under 8 ft | 4×4 (light loads) or 6×6 |
| 8–14 ft | 6×6 |
| Over 14 ft | 6×6 or engineered post |
For decks over 10 feet above grade, consult a structural engineer for post and beam sizing.
- Light loads, small deck, 6-ft spans: 10–12 inch diameter
- Typical residential deck: 12–16 inch diameter
- Heavy loads, hot tub, large cantilever: 16–24 inch diameter
- A 12-inch footing at 42 inches deep requires approx. 0.327 cubic feet of concrete (about half an 80 lb bag)
- Most jurisdictions require a permit for decks over 200 sq ft
- Decks attached to the house almost always require a permit
- Check with your local building department before breaking ground