Deck support post takeoff

Deck Post Calculator

Estimate deck support posts along simple beam lines, then convert the post-hole diameter and depth into concrete bag counts. Use it after the deck size is roughed in and before checking spans, loads, and footings.

Units

Deck length along beam (ft)Maximum post spacing (ft)Beam lines / post rows Hole diameter (in)Hole depth (in)Waste / extra concrete (%)Concrete yield per bag (ft³)Cost per post ($)Cost per concrete bag ($)

Posts to buy

Post spacing

Concrete bags

Rough cost

Deck posts need structural approval

This estimates post counts and concrete bags only. Beam spans, post size, footing diameter, frost depth, uplift, bracing, connectors, guard loads, soil, permits, and local deck code must be verified before building.

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Use a more detailed hole calculator for fence or deck post concrete.

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Roll deck boards, joists, railing, and labor into a rough deck total.

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Deck post formula

Posts per beam = ceiling(deck length ÷ max post spacing) + 1

Total post holes = posts per beam × beam lines

Hole volume = π × (diameter ÷ 2)² × depth

Concrete bags = holes × hole volume × (1 + waste %) ÷ bag yield

Sample takeoff

A 20 ft deck beam run with posts no more than 6 ft apart needs 5 posts per beam. Two beam lines need 10 holes, and 12 in by 36 in holes with 10% waste need about 44 bags at 0.6 ft³ per bag.A 6 m deck beam run with posts no more than 1.8 m apart needs 5 posts per beam. Two beam lines need 10 holes, and 300 mm by 900 mm holes with 10% waste need about 42 bags at 0.017 m³ per bag.

Deck Post Calculator FAQ

How do I calculate deck posts?+

Divide the beam run by your maximum post spacing, round up, add one end post, then multiply by the number of beam lines or post rows.Divide the beam run by your maximum post spacing, round up, add one end post, then multiply by the number of beam lines or post rows.

Does this choose the correct post spacing?+

No. The max spacing you enter must come from your beam span tables, deck plan, local code, or engineer.No. The max spacing you enter must come from your beam span tables, deck plan, local code, or engineer.

Can I use this for concrete bags under deck posts?+

Yes, for simple round post holes. Enter hole diameter, depth, and the concrete yield printed on the bag.Yes, for simple round post holes. Enter hole diameter, depth, and the concrete yield printed on the bag.