# Rebar

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.

- Category page: https://jianzhujisuan.com/en/c/rebar
- Data checked: 2026-10-25

## Tools in this group

- [Rebar Weight Calculator](https://jianzhujisuan.com/en/rebar-weight): Pick a bar diameter, enter length and quantity to get weight per metre, per bar and total tonnage.
- [Rebar Anchorage Length Calculator](https://jianzhujisuan.com/en/rebar-anchorage): Basic and seismic anchorage length from bar grade, diameter and concrete class.
- [Rebar Lap Length Calculator](https://jianzhujisuan.com/en/rebar-lap): Lap length ll / llE by splice percentage, plus the permitted number of splices.
- [Rebar Cut Length Calculator](https://jianzhujisuan.com/en/rebar-cut-length): Cut length and bar weight with standard hook allowances.
- [Rebar Spacing and Bar Count Calculator](https://jianzhujisuan.com/en/rebar-spacing): Bars and actual spacing from run length and design spacing, with total weight.
- [Stirrup Length and Count Calculator](https://jianzhujisuan.com/en/rebar-stirrup): Stirrup length, count and weight with the 11.9d seismic hook allowance.
- [Rebar Mesh Weight Calculator](https://jianzhujisuan.com/en/rebar-mesh): Weight per square metre and total mesh weight from dimensions and spacings.
- [Rebar Splice Percentage Calculator](https://jianzhujisuan.com/en/rebar-splice-ratio): Splice percentage at a section, code check and maximum permitted splices.
- [Rebar Bend Deduction Calculator](https://jianzhujisuan.com/en/rebar-bend-deduction): How much to deduct per bend when converting out-to-out to centreline length.
- [Rebar Hook Length Calculator](https://jianzhujisuan.com/en/rebar-hook-length): Added length for three hook types, with the seismic tail check.
- [Anchorage Length Modification Calculator](https://jianzhujisuan.com/en/rebar-anchor-modify): lab times correction factors, applying the no-combination rule for 0.8 and 0.7.
- [Reinforcement Ratio Calculator](https://jianzhujisuan.com/en/rebar-density-rate): ρ = As/(b·h0), and the reverse calculation for required steel.
- [Slab Rebar Quantity Calculator](https://jianzhujisuan.com/en/slab-rebar-quantity): Bar counts, total length and weight for two-way slabs.
- [Raft Foundation Rebar Calculator](https://jianzhujisuan.com/en/mat-rebar-quantity): Top and bottom layers plus stools in one calculation.
- [Mechanical Splice Calculator](https://jianzhujisuan.com/en/rebar-mech-joint): Splices and couplers from stock length, with the percentage check.
- [Rebar Stock Cutting Calculator](https://jianzhujisuan.com/en/rebar-stock-cut): Segments, offcut, purchase quantity and utilisation.
- [Rebar Quantity Estimator](https://jianzhujisuan.com/en/rebar-total-estimate): Floor area × steel rate for early-stage estimation.
- [Chair Bar Calculator](https://jianzhujisuan.com/en/chair-bar): Enter slab area, thickness and chair spacing to get the count, length per chair, total rebar length and weight.
- [Prestress Elongation Calculator](https://jianzhujisuan.com/en/prestress-elongation): Control stress, length and duct friction give elongation and loss.

## Questions

### 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.