Deck Framing Quantity Calculator
Joists = deck length in inches ÷ the joist spacing, rounded up, plus one: a 16 ft deck on 16 in centers takes 13 joists, and at 12 ft each that is 156 linear feet of joists.
Example: replace these measurements
Plan quantities
13 joist lines
13 joist lines
Your shopping list
- 13 joist lines
Quantities and package details
- Joist lumber before extra
- 156 linear ft
- Beam lumber from your plan
- 32 linear ft
- Post locations from your plan
- 3
- Post cut lengths combined
- 12 ft
- Joist and beam length with extra
- 188 linear ft
Quantity check only. Member sizes, allowable spans, loads, footings and connections must come from an accepted design.
The calculation
- ceil(16 × 12 ÷ 16) + 1 = 13 joist lines for a nonempty rectangle
- 13 × 12 = 156 linear ft of joists
Common questions
How many joists do I need for my deck?
Divide the distance across the joists by the joist spacing, round up and add one. At 16 inches on center, a 16-foot span takes 13 joists.
What size joists and beams do I need?
This calculator does not size them. The American Wood Council’s DCA 6 guide has span tables for its stated loads and materials, and your local building department decides what applies at your address.
How to plan the quantity
This is a quantity check for a prepared framing plan. Dividing the distance across joists by their spacing gives the bays; adding an edge line gives the joist count.
Beam lines, plies and post locations are entered from the plan. Multiplying their count by their length produces a lumber takeoff without pretending to choose an allowable span.
Keep joist size, species, grade, treatment, beam connections, ledger attachment, lateral support and footings with that plan. Each affects whether a deck design is suitable.
Before you order
- No structural member size, allowable span, footing dimension or load approval is calculated. A quantity result cannot establish that the design is safe.
- The AWC deck guide has stated material, load and jurisdiction limits. Ask the local building department or designer which provisions apply before ordering structural lumber.
Before ordering, read the guide: How many deck boards do I need? Boards, gaps and screws. Or choose another calculator.