Deck Footing and Post Layout Calculator
Create a preliminary material estimate and evenly spaced layout for deck support posts and concrete footings.
To estimate a preliminary deck-post layout, divide the usable beam length by a user-confirmed maximum post spacing, round up to find the number of bays, and add one post. Multiply the posts per row by the number of supported rows. Final spacing and footing design must be verified for the project’s loads, soil, plans, and local requirements.
Deck and Support Layout
Enter only rows supported by posts and footings. Do not count a house ledger as a post row.
Use a maximum spacing taken from approved plans, applicable span tables, manufacturer instructions, or a qualified professional. The calculator does not determine an allowable structural spacing.
Distance from each end of the beam line to the first and last post centerline.
Estimate Footing Concrete
Would you like to calculate footing dimensions, concrete volume, bags, and optional concrete cost?
Optional Post and Connector Cost
The partial estimate excludes excavation, reinforcement, inspection, delivery, equipment, labor, permits, engineering, and unpriced materials.
Your Estimate
Deck Area
240.00 sq ft
Supported Post Rows
1 row
Usable Layout Length
20.00 ft
Bays per Row
3 bays
Posts per Row
4 posts
Total Posts
4 posts
Total Footings
4 footings
Selected Maximum Spacing
8.00 ft
Actual Even Spacing
6.67 ft
Preliminary planning estimate only. The calculator evenly distributes posts along each entered row; it does not determine structural spans, beam-row locations, footing sizes, frost depth, or load capacity.
Results Actions
Post Centerline Positions
Positions are measured from the selected starting end. This same layout repeats for each of the 1 supported row.
| Post number | Position from start | Spacing to next post |
|---|---|---|
| 1 | 0.00 ft | 6.67 ft |
| 2 | 6.67 ft | 6.67 ft |
| 3 | 13.33 ft | 6.67 ft |
| 4 | 20.00 ft | — |
Deck Post and Footing Planning Information
This reference identifies inputs and design variables; it does not publish universal footing sizes, depths or post-spacing limits. Obtain project-specific structural and foundation requirements before using the estimator.
How to Use the Deck Footing and Post Layout Calculator
- 1Choose Imperial or Metric measurements; the calculator loads practical native defaults for the selected system.
- 2Enter the deck length along the beam direction and the deck projection or width. Width is used only for deck area and project context.
- 3Enter only the number of beam/post rows supported by posts and footings. Do not count a house ledger.
- 4Enter a maximum post spacing confirmed by approved plans, applicable span tables, manufacturer instructions or a qualified professional.
- 5Enter the equal setback from each beam end to the first and last post centerline.
- 6Optionally enable footing concrete and enter the already-established footing shape, dimensions, depth and published yield per bag.
- 7Choose a waste allowance and optionally enter current prices for concrete bags, posts and post bases or connectors.
- 8Review the evenly distributed position table and repeat those positions for each selected supported row.
- 9Verify the final layout, footing dimensions, frost protection, connections and permits before ordering or building.
Deck Post Layout and Footing Volume Formulas
- 1Deck area = deck length × deck projection or width.
- 2Usable post-layout length = deck length − (2 × equal end setback). Combined setbacks must remain less than the beam-line length.
- 3Bays per row = usable length ÷ user-selected maximum spacing, rounded up. At least one bay is required.
- 4Posts per row = bays per row + 1. Total posts = posts per row × supported post rows. Total footings = total posts.
- 5Actual evenly distributed spacing = usable length ÷ bays per row. Post position = end setback + (position index × actual spacing).
- 6Round footing volume = π × (diameter ÷ 2)² × depth after converting all dimensions to feet or meters.
- 7Square footing volume = width × length × depth after converting all dimensions to feet or meters.
- 8Base concrete volume = volume per footing × total footings. Waste-adjusted volume = base volume × (1 + waste percentage ÷ 100).
- 9Concrete bags = waste-adjusted volume ÷ published volume yield per bag, rounded up. Nominal bag weight is never used as a substitute for volume yield.
- 10Post cost = total posts × entered post price. Connector cost = total posts × entered connector price. Bag cost = rounded bags × entered bag price.
- 11Partial estimated material cost is the sum of enabled and user-priced posts, connectors and concrete bags only.
Imperial and Metric Deck Post Layout Examples
Imperial example (planning values, not recommendations): a user supplies a 20 ft beam-line length, 12 ft deck projection, 2 supported rows, 8 ft maximum post spacing, 1 ft end setbacks, round 12 in × 36 in footings, 10% waste and a product yield of 0.60 cu ft per bag. Usable length is 18 ft; ceiling(18 ÷ 8) gives 3 bays, 4 posts per row and 6 ft actual spacing. The 2 rows need 8 posts and footings. Each footing is about 2.36 cu ft; base concrete is 18.85 cu ft and 20.73 cu ft after waste, requiring 35 bags. At hypothetical entered prices of $15 per post, $12 per connector and $7 per bag, partial cost is $461. Metric example (planning values, not recommendations): a user supplies a 6 m beam line, 3.5 m projection, 2 rows, 2.4 m maximum spacing, 0.3 m end setbacks, round 300 mm × 900 mm footings, 10% waste and a published 0.0135 m³ yield per bag. Usable length is 5.4 m; 3 bays produce 4 posts per row at 1.8 m actual spacing and 8 total footings. Each footing is about 0.064 m³; base volume is about 0.509 m³ and waste-adjusted volume is about 0.560 m³, requiring 42 bags. Hypothetical user-entered prices can be applied to those whole quantities for a partial cost.
Accuracy & Assumptions
- The calculator is a preliminary layout and material estimator, not a structural design tool.
- Deck projection or width affects only displayed deck area; it never selects or spaces beam rows.
- Every supported row is assumed to use the same beam-line length, equal end setbacks and evenly distributed post layout.
- The user supplies an allowable maximum post spacing established for the project; the calculator does not select one.
- A house ledger is not counted as a supported post row, and the calculator does not evaluate ledger attachment or flashing.
- Footing shape, width, diameter, length and depth are user-supplied approved planning inputs, not recommendations.
- Footing volume treats each footing as a full, uniform cylinder or rectangular prism and does not subtract posts, bells, voids or reinforcement.
- Soil loss, over-excavation and placement variation are represented only by the selected concrete waste allowance.
- Bag quantity uses the displayed or custom published volume yield and rounds the final quantity up to whole bags.
- Approximate preset yields are planning defaults shared with existing project calculators; replace them with the selected product’s published yield.
- No concrete weight is shown because nominal bag weight alone does not verify the placed-volume density or exact product quantity.
- Partial cost includes only entered prices for posts, connectors and enabled concrete bags; blank prices are omitted.
- Excavation, reinforcement, inspection, delivery, equipment, labor, permits, tax, engineering and other materials are excluded.
- Displayed distances and volumes are rounded for readability while calculations use unrounded values.
Frequently Asked Questions
How many deck posts do I need per beam row?
Subtract both end setbacks from the beam-line length, divide by your project-confirmed maximum spacing, round up for bays and add one post.
Does this calculator choose safe deck-post spacing?
No. Enter spacing from approved plans, applicable span tables, current manufacturer instructions or a qualified professional.
Should I count the house ledger as a post row?
No. Count only rows supported by posts and footings. Ledger attachment and flashing require separate project-specific verification.
Does deck width determine the number of beam rows?
No. Width is used only for area and context. Enter the supported row count from the approved structural layout.
How are post positions calculated?
The calculator distributes the usable length into equal bays and measures each post centerline from the chosen starting end.
Can the two end setbacks be different?
This version uses one equal setback at both ends. For unequal conditions, prepare a project-specific field layout and verify every bay.
Does the calculator choose a footing diameter or depth?
No. Enter dimensions already established from loads, soil bearing, frost depth, plans and local requirements.
Why does concrete bag calculation use yield instead of bag weight?
Products with the same nominal weight can have different placed-volume yields. Published volume yield is the appropriate basis for bag quantity.
Why should I confirm the default concrete yield?
Preset yields are approximate planning values. Product formulation, water demand and packaging vary, so use the current package or data sheet.
What does the waste allowance cover?
It provides a planning buffer for minor excavation variation, handling loss and placement variation; it does not replace site measurement.
What is included in the material cost?
Only items you price: posts, post bases or connectors and, when enabled, whole concrete bags. The result is labeled as partial.
Does the estimate include excavation or reinforcement?
No. Excavation, rebar, forms, inspection, delivery, equipment, labor, permits, engineering and other materials are excluded.
Can I use the same layout for every supported row?
The result assumes all selected rows share the same length and setbacks. Do not use it where approved row layouts or site conditions differ.
Can I use this result for a permit drawing?
No. It is a conceptual planning estimate, not a construction drawing, engineering analysis or demonstration of code compliance.
This calculator provides a preliminary post-layout and partial material estimate only. It does not select or verify structural spans, beam sizes, joist sizes, post sizes, supported beam-row locations, footing dimensions, reinforcement, concrete strength, frost depth, soil bearing capacity, uplift resistance, bracing, lateral loads, connections or load paths. Deck requirements vary with loads, height, soil, climate, wind, seismic conditions, attached or freestanding construction, adopted code, local amendments and approved plans. Confirm underground utilities before excavation. Obtain required permits and inspections, and have the complete layout and foundation design verified by the local building department and a qualified designer, contractor or engineer before ordering materials or building.