1 Your measurements

Type feet and inches the way you'd write them, like 12' 6" or 30 3/8. Decimals work too.

ft
ft
in
Center to center, from your plans or local code.
in
How far the bars stop short of the slab edge. The last bar may land a little farther in.
in
Only needed when a bar is longer than one stick. Take it from your plans.

2 What to buy

Rebar to buy
22 sticks
20 ft #4 (½") bars
Total length
317 ft
22 bars in a grid
Weight
212 lb
at 0.668 lb per foot
Bars running the length8 bars × 19.5 ft
Bars running the width14 bars × 11.5 ft
Spacing18" each way, held 3" back from the edges
Crossings to tie112

The residential code requires slab reinforcement to be supported so it stays between the center and the upper third of the slab while the concrete is placed. Chairs or other supports under the grid hold it there.

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