Ceiling Joist Calculator
Check if a ceiling joist is adequate for a given span based on lumber size and spacing.
How to Use the Ceiling Joist Calculator
- Enter the span (distance between supports) in metres.
- Select the joist spacing.
- Select the lumber size.
- Click Calculate to see maximum allowable span and adequacy.
Use Cases
- •Residential ceiling framing design.
- •Checking existing ceiling structure.
- •Renovation planning.
- •Timber framing education.
Formula
Maximum spans from IRC span tables: 2×6@400=3.6m, 2×8@400=4.8m, 2×10@400=6.1m (reduced ~15% at 600mm).
Frequently Asked Questions
What species does this assume?
Values are approximate for No.2 Douglas Fir or equivalent. Consult local span tables for your species.
What load is assumed?
Spans assume residential ceiling loads (10 psf dead + 10 psf live).
What if the joist is not adequate?
Use a larger size (e.g., 2×10 instead of 2×8) or reduce the spacing from 600 to 400 mm.