Floor Joist Count — 24 ft Span, 24" OC, 12 ft Members
Determine how many 12-foot floor joists are needed across a 24-foot span at 24 inches on center.
How to use this tool
- Enter the total wall or floor span in feet.
- Set the on-center spacing (16 in or 24 in are most common).
- Enter the individual member length in feet.
- The result shows the number of members and total board linear footage to purchase.
Find the number of floor joists for a typical room addition or deck framing project.
Frequently asked questions
- How many studs do I need for a wall?
- Divide the wall length by the stud spacing (in feet) and add 1 for the end stud. Add 10% for waste, corners, and headers. For a 20 ft wall at 16 in OC: (20 ÷ 1.33) + 1 = 16 studs, plus 10% waste = 18 studs.
- What is 16-inch OC spacing?
- OC stands for on-center — the distance from the center of one stud to the center of the next. 16-inch OC is the standard for exterior walls and load-bearing walls; 24-inch OC is used in non-load-bearing walls to save lumber.