Framing Lumber Calculator
Calculate how many studs or joists you need to frame a wall or floor, based on spacing and length.
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.
Calculate how many studs or joists to buy for wall or floor framing.
Formula
Members (base) = ⌈span ÷ spacing_ft⌉ + 1
Members (with waste) = ⌈base_members × (1 + waste% ÷ 100)⌉
Total linear ft = members_with_waste × member_length
How it works
The calculator divides the total span by the on-center spacing (converted from inches to feet) and adds one for the starting member — reflecting the standard framing rule that a span of N spaces requires N+1 members. A waste percentage is then applied and the result rounded up before multiplying by the member length to get total board-feet ordered.
This formula covers a single straight wall or floor run. L-shaped rooms, openings that require headers and cripple studs, or double top plates will increase lumber requirements beyond this estimate.
Worked example
Worked example
- Spacing in feet = 16 in ÷ 12 = 1.333 ft.
- Base members = ⌈20 ÷ 1.333⌉ + 1 = ⌈15⌉ + 1 = 16 + 1 = 17 (note: ⌈15.0⌉ = 15, so 15 + 1 = 16… rechecking: 20 ÷ 1.3333 = 15, ceil = 15, + 1 = 16).
- With 10% waste: ⌈16 × 1.10⌉ = ⌈17.6⌉ = 18 members.
- Total linear feet = 18 × 8 ft = 144 ft.
Members needed: 18; Total linear feet: 144 ft
Key terms
- Stud
- A vertical framing member in a wall, typically 2×4 or 2×6 lumber, spaced 16 in or 24 in on center to support loads and provide a nailing surface for sheathing and drywall.
- On-center (OC) spacing
- The distance from the centerline of one framing member to the centerline of the next. Common wall-stud spacing is 16 in OC; floor joists are often 12, 16, or 24 in OC.
- Joist
- A horizontal framing member that spans between beams or walls to support a floor or ceiling. Joists are sized based on span length and load.
- Top plate
- The horizontal lumber member nailed across the tops of wall studs. Most walls use a double top plate, which is not accounted for in a simple stud count.
- Linear foot (LF)
- A measurement of length along a single dimension, used to price and order lumber. One linear foot of 2×6 lumber is 1 ft long regardless of its cross-sectional size.
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.