Rebar Calculator — bars, laps and spacing check
Bar count and weight for a slab, including the lap splices most calculators omit and a check against the ACI 318 maximum spacing.
Rebar Calculator — bars, laps and spacing check
Bar count and weight, plus the two things most rebar calculators leave out: the lap splices that make your order longer than the slab, and whether your spacing passes the code maximum.
| Bars each way | — |
|---|---|
| Net bar length | — |
| Lap splice length | — |
| Total length to buy | — |
| Stock bars | — |
| Weight | — |
| Code maximum spacing | — |
Bar weights are the standard nominal figures — #3 at 0.376, #4 at 0.668, #5 at
1.043 and #6 at 1.502 lb per foot. Bars each way are (dimension − 2 × cover) ÷ spacing + 1.
Maximum spacing for slab reinforcement under ACI 318 is the lesser of three times the slab
thickness or 18″, so a 4″ slab caps at 12″ on centre. That is a maximum, not a design:
the actual size and spacing come from the engineer of record, and this page only tells you whether the
number you typed is inside the ceiling.
Lap length is entered here as a multiple of bar diameter because the real value depends on
concrete strength, bar grade, coating, position and confinement. Forty diameters is a common
placeholder, not a specification — take the lap from your drawings. This estimates material for
a flat slab on grade; footings, walls, beams, hooks, chairs and tie wire are separate.