Rebar calculators

19 rebar calculators: theoretical weight, anchorage length and modification factors, lap length, cutting length, spacing and bar count, stirrups, mesh, splice percentage, bend deduction and tendons.

19 tools, most used first

≡Rebar Weight CalculatorPick a bar diameter, enter length and quantity to get weight per metre, per bar and total tonnage.≡Rebar Anchorage Length CalculatorBasic and seismic anchorage length from bar grade, diameter and concrete class.▭Rebar Cut Length CalculatorCut length and bar weight with standard hook allowances.⇄Rebar Lap Length CalculatorLap length ll / llE by splice percentage, plus the permitted number of splices.⌐Chair Bar CalculatorEnter slab area, thickness and chair spacing to get the count, length per chair, total rebar length and weight.▦Rebar Mesh Weight CalculatorWeight per square metre and total mesh weight from dimensions and spacings.⋮Rebar Spacing and Bar Count CalculatorBars and actual spacing from run length and design spacing, with total weight.▣Stirrup Length and Count CalculatorStirrup length, count and weight with the 11.9d seismic hook allowance.⇉Rebar Splice Percentage CalculatorSplice percentage at a section, code check and maximum permitted splices.⌐Rebar Bend Deduction CalculatorHow much to deduct per bend when converting out-to-out to centreline length.⌇Rebar Hook Length CalculatorAdded length for three hook types, with the seismic tail check.⌗Anchorage Length Modification Calculatorlab times correction factors, applying the no-combination rule for 0.8 and 0.7.▦Reinforcement Ratio Calculatorρ = As/(b·h0), and the reverse calculation for required steel.▩Slab Rebar Quantity CalculatorBar counts, total length and weight for two-way slabs.▬Raft Foundation Rebar CalculatorTop and bottom layers plus stools in one calculation.⊶Mechanical Splice CalculatorSplices and couplers from stock length, with the percentage check.⊓Rebar Stock Cutting CalculatorSegments, offcut, purchase quantity and utilisation.⊞Rebar Quantity EstimatorFloor area × steel rate for early-stage estimation.⋯Prestress Elongation CalculatorControl stress, length and duct friction give elongation and loss.

What this group solves

Two chains run through this group: weight and length. The weight chain starts from theoretical weight (d²/162) and extends to mesh, slabs, rafts and chair bars up to total tonnage. The length chain starts at anchorage, passes through laps, hooks and bend deductions, and ends at cutting length and stock optimisation — a cutting error is not a small overrun, it is a whole batch of scrap.

Every length tool follows the code: basic anchorage length times the modification factor, then times the seismic factor. Lap length is anchorage times 1.2, 1.4 or 1.6 depending on the percentage spliced at a section. Each parameter line states which clause it comes from — read that line before changing a factor, because this is the highest-rework category on the site.

FAQ

How is rebar weight calculated?

Theoretical weight in kg/m is 0.00617 × diameter², i.e. d²/162. That gives 0.888 kg/m for 12 mm, 2.47 kg/m for 20 mm and 3.85 kg/m for 25 mm, based on 7850 kg/m³ steel density. Actual weighed stock differs by 1-3%; settlement usually uses theoretical weight while purchasing should add a margin.

What is the difference between anchorage and lap length?

Anchorage is the length needed to develop the bar in the concrete and depends on bar profile, steel grade, concrete strength and seismic class. Lap length is anchorage multiplied by a splice factor: 1.2 for up to 25% spliced at a section, 1.4 for 50%, 1.6 for 100%. They are not interchangeable — a lap is always longer than an anchorage.

Why deduct for bends when cutting?

Drawings dimension the outside of the bend, but bending stretches the outside and compresses the inside; only the centreline length is what you cut. A 90° bend deducts roughly 2d — 40 mm on a 20 mm bar — and a beam with dozens of bends accumulates tens of centimetres of error. Cutting length = sum of outside dimensions − bend deductions + hook allowances.

Related data tables

Rebar weight tableEvery bar size from 6 mm to 40 mm: kg per metre, weight per 9 m and 12 m bar, metres per tonne.

Other groups

Concrete Masonry Finishes Earthwork Temporary Works Construction Costing M&E Material weights Area and volume Unit conversion Code Lookup

Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.