Calculate bar counts, cutting lists, total weight and lap lengths for slabs, beams, columns and mesh. Metric and imperial, standard bar sizes only, waste allowance included, and the exact formula printed with every result.
- Slab & Area
- Beam & Column
- Direct Entry
- Mesh Sheet
- Lap Lengths
- Cutting Lists
Use this mode when you already have a cutting list or a supplier quote and just need the total weight.
Standard mesh sheets are 6 m × 2.4 m = 14.4 m². A 10% overlap allowance is typical for standard lapped sheets on a slab.
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Cutting list summary
Bar Weight Reference
The accepted unit weights for standard rebar sizes. These are nominal values — actual weights can vary by the tolerance in the manufacturing standard (typically ±4% to ±6%).
| Metric size | kg/m | Imperial bar | lb/ft | Typical use |
|---|---|---|---|---|
| 6 mm | 0.222 | — | 0.149 | Stirrups, mesh, light slab |
| 8 mm | 0.395 | #3 (3/8") | 0.376 | Slab, links, mesh |
| 10 mm | 0.617 | — | 0.415 | Slab, wall, links |
| 12 mm | 0.888 | #4 (1/2") | 0.668 | Slab, wall, beam links |
| 16 mm | 1.579 | #5 (5/8") | 1.043 | Beam, column, footing |
| 20 mm | 2.466 | #6 (3/4") | 1.502 | Beam, column, footing |
| 25 mm | 3.854 | #8 (1") | 2.670 | Heavy beam, column |
| 32 mm | 6.313 | #10 (1-1/4") | 4.303 | Heavy column, pile, base |
| 40 mm | 9.864 | #11 (1-3/8") | 5.313 | Pile, bridge deck, heavy base |
How to Calculate Rebar Weight
Every rebar calculation comes back to one formula. Everything else is a way to count bars and measure their length.
Unit weight
The weight of one metre of bar at a given diameter.
w = d² ÷ 162.2 (kg/m)
Total length
Count the bars, multiply by the length of each, add lap allowances.
L = bars × length × (1 + laps)
Total weight
Multiply total length by unit weight.
W = L × w
Lap length
The overlap required when one bar cannot reach. Depends on concrete grade and bar diameter.
Lap = k × d (k from 30 to 45)
The d² ÷ 162 rule gives the accepted nominal weight. Actual bar weight varies within the standard — BS 4449 allows ±4.5% on a single bar, ASTM A615 allows ±6%. Always add a waste allowance (5% typical) when ordering.
Worked Rebar Examples from Site
| Task | Given | Calculation | Result |
|---|---|---|---|
| Slab mesh (both ways) | 10 m × 8 m, T10 @ 200 mm | 41 bars × 10 m + 51 bars × 8 m | 818 m = 505 kg |
| Beam longitudinal | 4 × T16, 6 m span | 4 × 6 m × 1.579 kg/m | 37.9 kg |
| Column main bars | 8 × T20, 4 m high | 8 × 4 × 2.466 | 78.9 kg |
| Beam links | T8 @ 150 mm, 300 × 500, 6 m span | 41 links × 1.72 m × 0.395 | 27.9 kg |
| Footing mat | 2.4 × 2.4 m, T12 @ 200 both ways, single | 13 × 2.4 + 13 × 2.4 = 62.4 m | 55.4 kg |
| Direct order | 200 × T12 @ 6 m | 200 × 6 × 0.888 | 1065.6 kg |
| Mesh sheet | A252 over 500 m² with 10% overlap | 500 × 1.98 × 1.10 | 1089 kg |
| Lap allowance | T16, C30/37, 5 laps | 5 × 37 × 16 = 2960 mm | +2.96 m of bar |
Lap and Development Length Reference
When a bar cannot reach, it overlaps with the next bar. The lap length depends on bar diameter, concrete grade and steel grade. Values below are simplified tension lap lengths — always confirm against the project specification and local code.
| Concrete grade | Lap factor (× d) | Example T16 lap | Example T20 lap | Example T25 lap |
|---|---|---|---|---|
| C20/25 (3000 psi) | 45 × d | 720 mm | 900 mm | 1125 mm |
| C25/30 (3600 psi) | 40 × d | 640 mm | 800 mm | 1000 mm |
| C30/37 (4350 psi) | 37 × d | 592 mm | 740 mm | 925 mm |
| C35/45 (5000 psi) | 35 × d | 560 mm | 700 mm | 875 mm |
| C40/50 (5800 psi) | 33 × d | 528 mm | 660 mm | 825 mm |
| C45/55 (6500 psi) | 30 × d | 480 mm | 600 mm | 750 mm |
Development length is typically taken as 1.3 × the tension lap length for standard conditions. In seismic zones and where bars are in tension at supports, higher factors apply — always refer to the structural drawings.
Rebar Standards and Tolerances
BS 4449
UK specification for steel for reinforcement of concrete. Nominal mass tolerance ±4.5% per bar.
ASTM A615
US specification for deformed and plain carbon-steel bars. Standard sizes #3 to #18.
ASTM A706
US specification for low-alloy deformed bars for seismic applications.
EN 10080
European specification for weldable reinforcing steel. Governs B500B and similar grades.
ACI 318
US code for structural concrete. Governs lap and development lengths.
Eurocode 2 (EN 1992-1-1)
European design code. Governs anchorage and lap lengths based on bond stress.
AS/NZS 4671
Australian and New Zealand steel reinforcing materials standard.
IS 1786
India specification for high-strength deformed bars. Grades Fe415, Fe500, Fe550.
SANS 920
South African steel bars for concrete reinforcement standard.
GSO / SASO standards
Gulf conformity specifications for imported reinforcing steel.
For quick site estimates, remember these unit weights: T10 = 0.617 kg/m, T12 = 0.888 kg/m, T16 = 1.58 kg/m, T20 = 2.47 kg/m, T25 = 3.85 kg/m, T32 = 6.31 kg/m. A 12 m stock length of T16 weighs 18.95 kg. Order 5% extra for wastage on cut-and-bend work and 10% on complex shapes with multiple bends.
People Also Ask
How do I calculate the weight of rebar?
Use the formula weight (kg/m) = d² ÷ 162.2 where d is the bar diameter in millimetres. For example, T16 = 256 ÷ 162.2 = 1.579 kg/m. Multiply by the total length in metres to get total weight. This is the accepted nominal weight used across construction.
What is the weight of a T12 rebar per metre?
0.888 kg per metre for T12. A standard 6 m bar weighs 5.33 kg, a 12 m bar weighs 10.66 kg. This is the most common slab and wall reinforcement size in metric construction.
How many bars in 1 tonne of T16 rebar?
T16 weighs 1.579 kg/m. A 12 m stock bar weighs 18.95 kg. One tonne = 52.8 bars of 12 m, or about 105 bars of 6 m. For T12: about 93 bars of 12 m per tonne. For T20: about 33 bars of 12 m per tonne.
What is the lap length for rebar?
Lap length depends on concrete grade, steel grade and bar diameter. For standard conditions, use a factor of 40 × d for C25/30, 37 × d for C30/37 and 35 × d for C35/45. Example: T16 in C30/37 concrete needs a 592 mm lap. Always confirm against the structural drawings — seismic zones and heavily loaded members require longer laps.
How do I calculate rebar for a slab?
For a slab with both-way reinforcement at spacing s: bars in one direction = ceil(width ÷ s) + 1, each with the length of the slab. Repeat for the other direction. If you have top and bottom layers, double the total. Add lap allowance for long slabs — typically a 40 × d overlap every 12 m stock length.
What is the difference between A142, A193 and A252 mesh?
The A numbers refer to the cross-sectional area of the mesh in mm²/m. A142 = 1.11 kg/m², A193 = 1.51 kg/m², A252 = 1.98 kg/m², A393 = 3.08 kg/m². Higher A number means more steel per square metre. A142 is for crack control in light slabs, A252 is standard slab mesh, A393 is for heavier loading.
How much does a 6 m rebar weigh?
Depends on diameter. T10 = 3.70 kg, T12 = 5.33 kg, T16 = 9.47 kg, T20 = 14.80 kg, T25 = 23.12 kg, T32 = 37.88 kg. Multiply the per-metre weight by 6 to get the stock bar weight.
What is the minimum cover for rebar?
Cover depends on exposure conditions. For interior, protected concrete: 20 mm. For exposed to weather: 40 mm. For cast against earth (footings): 75 mm. For marine or chemical exposure: up to 50–60 mm. Always check ACI 318 or EN 1992 exposure class tables — insufficient cover is the leading cause of rebar corrosion.
Why is the number 162 used in the rebar formula?
It comes from the density of steel (7850 kg/m³) and the geometry of a cylinder. Weight per metre = π × (d/2)² × 1 × 7850 ÷ 1,000,000. Simplifying gives d² × 0.006166 = d² ÷ 162.2. The exact constant is 162.28 but 162 is used on site for mental maths because the difference is under 0.2%.
Does the calculator include lap lengths and bends?
The lap length is calculated and shown in the results — it is based on your concrete grade and the bar diameter. Bend deductions are not included because they vary with bend radius and shape code. Add a waste allowance (5% typical, 10% for complex cut-and-bend) to cover bends, laps and offcuts in the order quantity.
Related Calculators
References
- British Standards Institution. BS 4449: Steel for the Reinforcement of Concrete — Weldable Reinforcing Steel. BSI.
- ASTM International. ASTM A615/A615M — Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement. ASTM.
- ASTM International. ASTM A706/A706M — Standard Specification for Deformed and Plain Low-Alloy Steel Bars for Concrete Reinforcement. ASTM.
- European Committee for Standardization. EN 10080: Steel for the Reinforcement of Concrete — Weldable Reinforcing Steel. CEN.
- American Concrete Institute. ACI 318: Building Code Requirements for Structural Concrete — Development and Splices of Reinforcement. ACI.
- European Committee for Standardization. EN 1992-1-1: Eurocode 2 — Design of Concrete Structures, Part 1-1: General Rules and Rules for Buildings. CEN.
- Standards Australia / Standards New Zealand. AS/NZS 4671: Steel for the Reinforcement of Concrete. SAI Global.
- Bureau of Indian Standards. IS 1786: High Strength Deformed Steel Bars and Wires for Concrete Reinforcement. BIS.
- South African Bureau of Standards. SANS 920: Steel Bars for Concrete Reinforcement. SABS.
- International Organization for Standardization. ISO 6935-2: Steel for the Reinforcement of Concrete — Part 2: Ribbed Bars. ISO.
Confirm all rebar quantities, lap lengths and cover against the structural drawings and local code before ordering or fabrication.