How many deck joists and footings do I need?
Use regular spacing inputs to make an early joist or footing grid easy to check.
Short answer
Measure the run or perpendicular dimension, choose the maximum spacing from the framing plan, and count the whole spaces plus the boundary member or footing.
For homeowners comparing a regular deck framing layout before structural review.
How to do it
Measure the layout dimension
Use the dimension across joists for the joist tool, or the run covered by one footing row for the footing tool.
Choose maximum spacing
Use the spacing from your deck plan, product information, or structural guidance.
Enter rows when needed
For footings, enter the number of parallel rows in the early grid.
Review before ordering
Use the count as a layout aid, then confirm span, soil, frost, loads, beams, and local requirements.
Formula
Round the measured dimension divided by maximum spacing up to whole spaces. Add one for joists or footings per row, then multiply footing count by row count.
Illustrative example
A 20 ft run at 6 ft maximum spacing has 4 spaces and 5 footings per row. Two rows produce 10 footings before any concrete calculation.
Common mistakes
- Using board direction instead of the perpendicular joist dimension
- Treating a regular grid as a structural approval
- Forgetting that a second footing row changes the total
Before you buy
Confirm framing members, species, grade, hangers, beams, blocking, footing size, bag yield, and inspection needs before buying.
What this guide does not cover
The tools do not verify span, load, deflection, beam sizing, ledger attachment, cantilever, frost depth, or code compliance.
Use the calculator
Deck Joist Calculator is the primary tool for this guide. You can also browse the other deck & outdoor calculators.