How to use
- Enter the slab length and width in feet.
- Enter the spacing in inches, center to center, the spacing the drawing asks for.
- Press Calculate. The hero is total feet of bar. The two counts are the bars parallel to each side.
- Add lap length yourself if a bar has to be spliced because it is longer than the stock you can buy.
How it's calculated
Bars parallel to the length: take the width in inches, divide by the spacing, round down, and add 1 so both edges are included. Each of those bars is as long as the slab length.
Bars parallel to the width use the length in inches the same way, and each is as long as the slab width. Total feet is the sum of both families. A spacing that lands exactly on the far edge does not add an extra bar beyond that edge.
Worked example
A 10 by 10 foot slab at 18 inch spacing needs 7 bars each way: 120 inches ÷ 18 is 6.67, which rounds down to 6, plus the starting bar is 7. Each bar is 10 feet, so the grid is 140 feet. No lap is included in the 140.
Assumptions
One rectangle, one spacing, bars in both directions, and a bar on each edge. Cover from the form edge to the first bar is not inset. If the drawing holds the first bar in from the form, shorten the span before you divide.
FAQ
Why plus one?
The first bar sits at the start. Dividing the span by the spacing counts the gaps, not the bars. Adding one turns gaps into bars and keeps a bar at the far side when the spacing divides evenly.
Does this include dowels or laps?
No. Add overlap length for every splice the supplier cannot deliver as a single bar.
Is this the concrete volume?
No. Cubic yards and bags are the concrete calculator on ClearQuip.
What if the spacing is different each way?
Run the page twice, once per spacing, and keep only the count for the direction that uses that spacing. This form uses one spacing for both ways.