Construction & Trade

Rebar Calculator

Construction & Trade

Rebar Calculator

Live answer348.7 ft8 bars across width · 14 bars across length

Slab length (ft)The longer direction of the slab, footing pad or rectangular concrete area.Slab width (ft)The shorter direction of the slab or pad.Rebar spacing (in on centre)Typical planning spacing between parallel bars. Engineering drawings override this calculator.Edge cover (in)Distance from slab edge to the first bar, used on both sides before spacing bars across the clear span.Lap and waste allowance (%)Planning allowance for laps, cuts, bends, breakage and site handling.Optional bar price ($/ft)Optional estimating price for a quick material-cost note. Leave as 0 if not needed.

Live result348.7 ft8 bars across width · 14 bars across length

Formula used

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.

Live math canvas

Your numbers, formula and explanation together

Rebar Calculator: 348.7 ft. 8 bars across width · 14 bars across length

Formula applied

The exact method behind this answer

CalculationTime keeps the method visible so the number can be checked instead of blindly 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).

Apply the formulaClear 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).348.7 ft8 bars across width · 14 bars across length

Your live breakdown

Current inputs in the calculation

These values come from the controls above and update when the calculator changes.

Slab length: 20 ft
Slab width: 12 ft
Rebar spacing: 18 in on centre
Edge cover: 3 in
Lap and waste allowance: 10 %
Optional bar price: 0 $/ft

Resulting answer

348.7 ft

8 bars across width · 14 bars across length

Answer: 348.7 ft
Live support: 8 bars across width · 14 bars across length

Assumptions used

What this answer assumes

Best for early material takeoffs, slab quote checks, owner-builder notes, classroom grid examples and job files where rebar assumptions need to be visible beside the quantity.

The calculator estimates a simple rectangular two-way rebar grid, not a certified structural design.
Spacing and edge cover are planning inputs; engineering drawings, local code and site inspection override any generic calculator result.
Bar length is measured inside the edge-cover line. It does not automatically add hooks, chairs, ties, dowels, mesh, bent bars or footing-specific reinforcement.
The lap/waste percentage is a procurement allowance for cuts, laps and handling; exact lap lengths depend on bar size, concrete strength, code and design details.

Master’s Tip

How to use the result well

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.

Printable record

What belongs in the saved calculation

Save the inputs, result, formula, assumptions, page URL and date together so the calculation can be reviewed later.

Slab length: 20 ft
Slab width: 12 ft
Rebar spacing: 18 in on centre
Edge cover: 3 in

Visual grid

This result measures part of the space you live in

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.

Micro-timehours, minutes, shiftsHuman scaledays, weeks, projectsMacro-timemonths, years, calendars

Measured output348.7 ft

Space calculations turn a real surface, room, run or volume into cells, edges and allowances that can be quoted, ordered or checked.

348.7 ft8 bars across width · 14 bars across length

Inputs

Slab length: 20 ft
Slab width: 12 ft
Rebar spacing: 18 in on centre
Edge cover: 3 in
Lap and waste allowance: 10 %
Optional bar price: 0 $/ft

Method

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.

Assumptions

The calculator estimates a simple rectangular two-way rebar grid, not a certified structural design.
Spacing and edge cover are planning inputs; engineering drawings, local code and site inspection override any generic calculator result.
Bar length is measured inside the edge-cover line. It does not automatically add hooks, chairs, ties, dowels, mesh, bent bars or footing-specific reinforcement.
The lap/waste percentage is a procurement allowance for cuts, laps and handling; exact lap lengths depend on bar size, concrete strength, code and design details.

Notes

Use this space on the printed report for client, supplier, classroom, job-location, measurement, quote or approval notes.