Calculation method
Set outside bar centers inward by clear cover plus half the bar diameter. For each direction, divide the opposite centerline span by maximum spacing, round intervals up, and add one end bar. Cut bar ends at clear cover; split each run into 20 ft pieces with the entered overlap, then count stock pieces without reusing offcuts.
Worked example: input to purchase quantity
A 24 ft × 12 ft slab with 12 in maximum spacing, 2 in cover, 0.5 in bars and 16 in laps has 13 lengthwise runs and 25 widthwise runs. Thirteen long runs need two stock pieces each; 25 short runs need one each, for 51 stock bars.
This calculator supports two-way slab rebar grid takeoff. Enter slab length and width, maximum bar spacing, clear edge cover, bar diameter, and a design-specified lap length. The arithmetic uses the values you provide and displays the purchase result alongside the intermediate amount. The output is intended for a measured planning worksheet; it does not replace a project drawing or product specification.
Measure and choose the correct input
Measure the actual slab edges and obtain cover, bar size, spacing, and lap from the drawing or responsible designer. The bar center is inward from the edge by cover plus radius, while each cut end stays inward by clear cover. A run exactly 20 ft needs one stock bar; one slightly longer needs a second and a lap.
How the estimate is calculated
Centerline span = slab dimension − 2 × (cover + half diameter); runs = ceiling(opposite span ÷ spacing) + 1; cut length = slab dimension − 2 × cover; each 20 ft stock joint overlaps by the entered lap. For 24 by 12 ft, the centerline inset is 2.25 in. Across the 12 ft width, 139.5 ÷ 12 rounds up to 12 spaces, so 13 long runs. Across 24 ft, 283.5 ÷ 12 rounds up to 24 spaces, so 25 short runs. Long cuts are 284 in; short cuts are 140 in. The long runs each use two 240 in stock pieces with a 16 in lap, while short runs use one each: 13 × 2 + 25 = 51 bars.
Verify the order
Sketch both bar directions and count end bars once per direction. Verify that the input is maximum center-to-center spacing, not the clear gap between neighboring bars. Confirm stock length and local supplier bar designation. The result intentionally assigns fresh stock to each run and treats offcuts as unavailable; a documented cut plan may lower the order.
Where the model ends
This is a one-layer rectangular quantity model. It does not design reinforcement, check development or splice location, account for bends, chairs, supports, waste, or optimize offcuts. Keep that limitation visible when using the quantity for a real purchase.
Keep a traceable worksheet
A useful order begins with a dated sketch, a product name, and dimensions recorded in their original units. Mark each repeated element so that its count can be checked against the site. Record where each figure came from: a tape measure, a plan, a supplier listing, or a design detail. This makes later changes auditable. If two sections differ, estimate them separately before adding the purchase quantities. A single average may hide a small but important difference at a boundary.
Read the result in stages
The calculator shows intermediate quantities so the final purchase count can be checked. Work through the displayed values in order instead of treating the last number as a guarantee. Keep full precision during the calculation and round only where the model says a purchasable whole item is required. A value just over a whole item still requires another item. If the answer changes after switching units, check whether converted entries were rounded in the form or whether a product-specific unit was assumed.
Separate quantity from design
This worksheet estimates material amounts from chosen project inputs. It cannot inspect the site or decide what assembly is safe and suitable. Structural requirements, local rules, product instructions, drainage, loads, and installation methods belong in the project design. Resolve those matters before treating a material estimate as a purchase list. If the design changes, update the dimensions and parameters and calculate again. Do not use an arbitrary extra percentage to repair an incorrect geometry or unsuitable specification.
Check the seller before paying
Compare the measured result with the unit in which the seller actually quotes and sells material. Check available stock sizes, package quantities, delivery constraints, return terms, and whether a listed size is nominal or actual. A quantity that is mathematically correct can still produce a wrong order when a product is sold by a different unit. Save the product page or label used for the estimate. If the listed yield, dimension, or unit price changes, revise the worksheet rather than reusing an old purchase count.
Product and method reference
Reference limits and default yields are identified separately from user-entered values; verify the adopted local code and current product label. CRSI reinforcing bar splicing guidance.
Calculation and editorial review: November 3, 2026. Arithmetic runs in your browser; project inputs are not submitted to TwoCut.