Construction & Trade
Estimate rebar pieces, total bar length and material cost for a rectangular slab or pad using spacing, edge cover, lap allowance and a printable job note.
Calculator
Clear length = slab length − 2 × cover. Clear width = slab width − 2 × cover. Bars across width = floor(clear width ÷ spacing) + 1. Bars across length = floor(clear length ÷ spacing) + 1. Total bar length = bars across width × clear length + bars across length × clear width. Order length = total bar length × (1 + lap/waste percent ÷ 100).
This is the method behind the answer, so the result can be checked rather than simply trusted.Visual grid
Length, area, volume and material estimates are grid problems too: measure the space, account for edges and allowances, then turn the pattern into a number you can use.
Space calculations turn a real surface, room, run or volume into cells, edges and allowances that can be quoted, ordered or checked.
CalculationTime
Clear length = slab length − 2 × cover. Clear width = slab width − 2 × cover. Bars across width = floor(clear width ÷ spacing) + 1. Bars across length = floor(clear length ÷ spacing) + 1. Total bar length = bars across width × clear length + bars across length × clear width. Order length = total bar length × (1 + lap/waste percent ÷ 100).
Use this space on the printed report for client, supplier, classroom, job-location, measurement, quote or approval notes.
Clear length = slab length − 2 × cover. Clear width = slab width − 2 × cover. Bars across width = floor(clear width ÷ spacing) + 1. Bars across length = floor(clear length ÷ spacing) + 1. Total bar length = bars across width × clear length + bars across length × clear width. Order length = total bar length × (1 + lap/waste percent ÷ 100).
For a 20 ft by 12 ft slab with 18 in spacing and 3 in cover, the clear length is 19.5 ft and the clear width is 11.5 ft. Bars across the width: floor(11.5 ÷ 1.5) + 1 = 8. Bars across the length: floor(19.5 ÷ 1.5) + 1 = 14. Total before allowance is 8 × 19.5 + 14 × 11.5 = 317 ft. With 10% allowance, order about 348.7 linear ft.
Master’s Tip: never let a rebar calculator replace the drawing. Use it to catch quantity mistakes, prepare a quote note or check a takeoff; use the engineer’s schedule for bar size, spacing, cover, laps, chairs and inspection requirements.
Standard or basis: rectangular grid takeoff arithmetic using feet, inches, on-centre spacing and edge cover. This is an estimating aid only and does not certify ACI, Eurocode, Australian Standard or local building-code compliance.
Methodology & Accuracy
CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.
Clear length = slab length − 2 × cover. Clear width = slab width − 2 × cover. Bars across width = floor(clear width ÷ spacing) + 1. Bars across length = floor(clear length ÷ spacing) + 1. Total bar length = bars across width × clear length + bars across length × clear width. Order length = total bar length × (1 + lap/waste percent ÷ 100).
Standard or basis: rectangular grid takeoff arithmetic using feet, inches, on-centre spacing and edge cover. This is an estimating aid only and does not certify ACI, Eurocode, Australian Standard or local building-code compliance.
Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.Master’s Tip: never let a rebar calculator replace the drawing. Use it to catch quantity mistakes, prepare a quote note or check a takeoff; use the engineer’s schedule for bar size, spacing, cover, laps, chairs and inspection requirements.
Subtract edge cover from both sides to get the clear length and width, divide each clear span by the spacing, add one bar for the starting line, then multiply each bar count by the bar run length.
Use the spacing shown on the engineering drawing or local requirement. This calculator accepts any spacing for estimating, but it does not decide structural spacing for you.
It includes a percentage allowance for laps and waste, but it does not calculate code-specific lap splice length. Exact lap rules depend on bar size, concrete strength, development length and design details.
Edge cover keeps steel away from the outside face of the concrete. In a takeoff, cover also reduces the clear grid length used for each bar run.
Print slab length, width, spacing, cover, bar counts both ways, total linear feet, lap/waste allowance, formula, assumptions, date and job notes so the takeoff can be checked before ordering.
Rebar takeoffs are grid calculations with a safety boundary. The arithmetic is simple, but the consequences are not: spacing, cover, lap, chairing and bar size belong to the structural design. A good printable estimate therefore keeps the calculator result separate from the professional design assumptions.
Bars running one way are spaced across the other dimension. That is why a rectangular slab needs two counts: bars that run lengthwise and bars that run widthwise.
Concrete cover helps protect reinforcement from exposure and corrosion. For estimating, the same cover distance also defines the clear bar run inside the slab edge.
A job note with dimensions, spacing, cover, allowance and bar counts is easier to compare with drawings, supplier quotes and site changes than a single unexplained total.