Calculate the span for floor and ceiling joist with this free and simple online calculator. The resulting spans are less than the 2012 IRC codes but they are to our standards at Scott’s Framing. The spans for joists according to the code is far more than we find acceptable. We have engineered this calculator to provide spans which will produce a solid built house with no bounce in the floors or any swags in the ceiling.

Joist Span Calculator

Select a load. There are six choices. The lowest is a plain ceiling joist with no storage (10 pounds per square foot). The highest is a fully loaded floor (70 pounds per square foot).
Select the on center spacing for the joists. This is how far apart they will be. Most lay outs are on 16″ so the field is pre-selected. To change it, click on another option.
Enter a span for the joist. This will be slightly less than the length of the board. For example; if a room is 10′ inside to inside and the joists are cut 10′ 7″ so they will bear fully on both walls, then the span will be 10′.
Finally, select a type of lumber. No. 2 pine is the the most common so the field is pre-selected at that. The other choices include spruce which is actually the spruce-pine-fir category, and the engineered I-joist.