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.
≡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.
Rebar is the hardest account to reconcile, because drawings give shapes and bar marks, not weight. The chain runs: count bars and their lengths from the marks, correct the cut length for bend deduction, multiply by the theoretical mass per metre, then add laps, anchorage and mechanical joints. Any mismatch in convention shows up as tonnes — and rebar is one of the few materials where over-ordering ties up cash and under-ordering stops the job.
Which one for your case
| Diameter, length and count known — need tonnage | Rebar Weight Calculator |
| Looking up seismic anchorage length lae | Rebar Anchorage Length Calculator |
| Lap length where the stagger ratio is not 25% | Rebar Lap Length Calculator |
| Cut lengths that must allow for 90° and 135° bend deduction | Rebar Bend Deduction Calculator |
| Estimating a whole slab or raft mat | Raft Foundation Rebar Calculator |
| Checking whether the reinforcement ratio is adequate or over-reinforced | Reinforcement Ratio Calculator |
| Planning cuts against 9 m or 12 m stock lengths | Rebar Stock Cutting Calculator |
Where this group goes wrong
- Cutting to the straight dimension on the drawing. Every 90° bend takes 2d of bend deduction, so a 12 m beam bar with two hooks is over-counted by about 0.2 m; a few hundred bars a floor adds up to tonnes of phantom steel.
- Reading the lap length straight from la and forgetting the stagger factor. At 50% lapped in one section multiply by 1.4, at 100% by 1.6, and never less than 300 mm. Miss this and the joint zone comes up 30% short.
- Taking stirrup length as the member perimeter. A 300×600 beam with 25 mm cover and Φ8 stirrups cuts at (300-50+600-50)×2 plus hooks — over 200 mm less than the perimeter. With dozens of stirrups per beam the error easily reaches 10%.
- Substituting d in centimetres into d²/162. The formula takes d in millimetres: Φ12 gives 0.888 kg/m. Using centimetres gives 88.8 kg/m, out by a factor of 100.
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.
Where does the theoretical mass per metre come from?
From d²/162 with d in millimetres — it is simply ρπd²/4 with ρ = 7850 kg/m³. Φ6=0.222, Φ8=0.395, Φ10=0.617, Φ12=0.888, Φ14=1.21, Φ16=1.58, Φ20=2.47, Φ25=3.85 kg/m. Schedules and settlement use this theoretical mass rather than weighbridge figures, so cutting lists should too or the two will not reconcile.
What is the difference between anchorage and lap length?
Anchorage (la, lae) is the length needed to transfer force from a bar into the concrete by bond. A lap (ll, llE) transfers force between two bars, and its length is the anchorage length multiplied by a stagger factor. A lap is therefore always at least as long as the anchorage, and never shorter than 300 mm.
Why does the stagger ratio change the lap length?
The more laps sit in one section, the harder it is for stress to pass through the concrete there, so a longer bond length is needed to compensate: 1.2 for 25% lapped, 1.4 for 50% and 1.6 for 100%. The common site error is applying 1.2 everywhere, which leaves congested joints short.
What waste allowance applies to reinforcement?
Standard schedules allow 2-3% for in-situ reinforcement and 3-5% for stirrups and miscellaneous bars, with mechanical couplers counted separately. That is the contract basis; with poor cutting against stock lengths the real loss can reach 6-8%, and running a cutting plan usually brings it back under 3%.
Related data tables
Other groups
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.