Steel Reinforcement Calculator UK | Mesh & Rebar
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Calculate mesh sheets needed, rebar weight per metre (d²÷162), and steel area per metre for any slab. Formulas, tables, and worked examples for UK projects.
| Bar Size | Diameter (mm) | Mass per Metre | Area per Bar (mm²) | NDS Price (6 m) |
|---|---|---|---|---|
| T8 | 8 | 0.395 kg/m | 50.3 | £3.05 |
| T10 | 10 | 0.617 kg/m | 78.5 | £3.15 |
| T12 | 12 | 0.888 kg/m | 113.1 | £6.79 |
| T16 | 16 | 1.579 kg/m | 201.1 | £10.95 |
| T20 | 20 | 2.466 kg/m | 314.2 | £17.58 |
| T25 | 25 | 3.854 kg/m | 490.9 | £25.43 |
| T32 | 32 | 6.313 kg/m | 804.2 | £41.70 |
| T40 | 40 | 9.864 kg/m | 1,256.6 | £65.10 |
| Bar Size | 300 mm CRS | 250 mm CRS | 200 mm CRS | 175 mm CRS | 150 mm CRS | 125 mm CRS |
|---|---|---|---|---|---|---|
| T10 | 262 | 314 | 393 | 449 | 524 | 628 |
| T12 | 377 | 452 | 565 | 646 | 754 | 905 |
| T16 | 670 | 804 | 1,005 | 1,149 | 1,341 | 1,609 |
| T20 | 1,047 | 1,257 | 1,571 | 1,795 | 2,094 | 2,513 |
| T25 | 1,636 | 1,963 | 2,454 | 2,805 | 3,272 | 3,927 |
How Do You Calculate How Many Mesh Sheets You Need?
Divide your total slab area in square metres by exactly 10, and then multiply by 1.1; this instantly accounts for the mandatory 200mm sheet overlap losses and a strict 10% cutting waste allowance.
Technical Specifications: The 4.8m x 2.4m Standard
- Nominal Size: A full sheet mathematically covers 11.52 m².
- Effective Coverage: Because structural codes mandate a minimum one-square (200mm) overlap where sheets meet, the true "safe" coverage drops to a flat 10 m² per sheet.
Application Rules
- The Golden Formula: Area (m²) ÷ 10 × 1.1 = Total Standard Sheets Required. Always round up to the nearest whole sheet. (E.g., 40m² ÷ 10 = 4. 4 × 1.1 = 4.4. Order 5 sheets).
Pro Tip: Do not use this standard 10m² rule if you are being forced to buy tiny 3.6m x 2m "merchant size" sheets from a local yard. Their effective coverage is only 6.5m², meaning a 60m² extension slab will suddenly require a massive 11 merchant sheets instead of just 7 standard ones.
How Do You Calculate Rebar Weight per Metre?
The universal, unchangeable mathematical constant for calculating the mass of any steel rebar in kg/m is simply dividing the bar's diameter squared by the fixed number 162.
Technical Specifications: The (d² ÷ 162) Formula
- T10 Rebar: 10 x 10 = 100. 100 ÷ 162 = 0.617 kg per metre.
- T12 Rebar: 12 x 12 = 144. 144 ÷ 162 = 0.888 kg per metre.
- T16 Rebar: 16 x 16 = 256. 256 ÷ 162 = 1.580 kg per metre.
Application Rules
- Logistical Tonnage: When scheduling a massive foundation pour, you must calculate total weight exactly. A small flatbed truck maxes out at roughly 1,500kg of payload before risking legal highway suspension failure.
Pro Tip: Let NextDaySteel's system calculate the weights for you. When you email your bar bending schedule, our immediate quote will list the exact metric weight per line item. This is critical for assessing whether your site requires a HIAB offload for safety compliance.
Mesh Sheet Quantity Calculator
Sheets = Slab area (m²) ÷ 10 × 1.1 (round up to next whole number)Rebar Weight per Metre
Mass (kg/m) = d² ÷ 162Steel Area per Metre Width
As (mm²/m) = (π × d² ÷ 4) × (1,000 ÷ spacing in mm)Total Order Weight
Total weight = Σ (Number of bars × Length × Mass per metre) + (Sheets × Sheet mass)Frequently Asked Questions
How many mesh sheets do I need for a 40 m² slab?
For 4.8 × 2.4 m standard sheets: 40 ÷ 10 × 1.1 = 4.4, round up to 5 sheets. The formula uses 10 m² effective coverage per sheet (11.52 m² nominal minus 200 mm overlaps) plus 10% for cutting waste.
How do I calculate rebar weight for delivery?
Use the formula: mass (kg/m) = d² ÷ 162, where d is the bar diameter in mm. Multiply by bar length to get weight per bar. Then multiply by quantity. Example: 20 × T16 bars at 4 m each = 20 × 4 × 1.579 = 126.3 kg.
What steel area does T12-200 provide?
T12 at 200 mm centres provides 565 mm²/m. The calculation: each T12 bar has a cross-sectional area of 113.1 mm² (π × 12² ÷ 4). At 200 mm centres, there are 5 bars per metre (1,000 ÷ 200). Steel area = 113.1 × 5 = 565 mm²/m.
How do I calculate reinforcement for a double-layer slab?
For top and bottom mesh (T&B), calculate sheets for one layer and multiply by two. A 60 m² slab with A193 top and bottom: single layer = 60 ÷ 10 × 1.1 = 6.6 → 7 sheets. Double layer: 7 × 2 = 14 sheets total.
What is the weight formula for rebar based on diameter?
Mass per metre (kg/m) = d² ÷ 162. This formula works for all standard rebar sizes from T8 to T40. It derives from steel density (7,850 kg/m³) and the circular area formula.
How much does reinforcement cost for a 60 m² extension?
A 60 m² raft foundation with A193 mesh top and bottom needs 14 sheets at £33.50 each (4.8 × 2.4 m from NDS) = £469.
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