Deck Joist Spacing
Calculate deck joist spacing from a few simple inputs generally.
About Deck Joist Spacing
Deck Joist Spacing — figures are approximate reference values; verify current rates and rules with the official source before relying on them.
Formula
Formula
Joists = floor(length × 12 ÷ spacing) + 1 + extras
Worked example
With the default values below, Deck Joist Spacing returns Joists Needed of 18. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Deck length (ft)accepts 0–100,000
- 20
- Joist spacing (in)accepts 6–48
- 16
- Extra joistsaccepts 0–20
- 2
Results
- Joists Needed
- 18
- Spacing (in)
- 16.0
Step by step
- 1Values used
- 2Formula
- 3Joists Needed= 18
- 4Spacing (in)= 16.0
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
- Reference estimate — verify with the official source.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Reference estimate — verify with the official source.
Frequently Asked Questions
Is this an official figure?
No — it is a reference estimate. Confirm rates, limits and rules with the official source.
How accurate is this estimate?
Rates are approximate reference values. Local rates, exemptions and rules can differ, so treat the output as a planning figure only.