Floor Joist Calculator
Estimate joist count and lumber for any floor frame.
Use this floor joist calculator to estimate joist count and lumber for any floor frame. It calculates total joist lumber from the floor width, joist spacing, and span length, then includes rim board and one row of mid-span blocking. Always confirm spans against local code and lumber species tables.
Joists
10
16 in OC
Joist lumber
200
linear ft
Rim + blocking
36
linear ft
Save this project
Sign in to save calculations to your dashboard.
Download your PDF report & project guide
Your results and inputs, a printable shopping list, a step-by-step guide and pro tips — in one PDF.
Planning a whole project?
Get every calculator, a full shopping list and a budget template for:
Recommended tools & materials
Handy picks for this project on Amazon.
Speed Square
Fast angle and rafter layout
View on Amazon →
Framing Nailer
Drive framing nails in seconds
View on Amazon →
Construction Screws
Structural, coated, no pilot hole
View on Amazon →
25 ft Tape Measure
Durable, easy-to-read blade
View on Amazon →
As an Amazon Associate, MaterialCalc earns from qualifying purchases.
How does the floor joist calculator work?
Joist count = (floor width in inches ÷ spacing) + 1. Total joist lumber = joists × span length. Add rim board (2× floor width) and one row of mid-span blocking.
What else do people ask about this calculator?
How far can a 2×10 joist span?
Roughly 15–17 ft at 16 in OC for #2 SPF residential floor loads. Always confirm with your local code and lumber species tables.
What is joist blocking for?
Solid blocking between joists at mid-span prevents rotation and stiffens the floor, especially for spans over 8 ft.
Which related calculators should I use next?
All calculators
Complete Your Floor Framing Project
These tools and fasteners help you cut, assemble, and secure floor joists efficiently.
DEWALT Framing Nailer
Search on Amazon →
Simpson Connector Screws
Search on Amazon →
IRWIN 10-inch Saw Blade
Search on Amazon →
Paid links: as an Amazon Associate, MaterialCalc earns from qualifying purchases.