H40 (40 mm) Reinforcing Bar - BS (UK)
H40 (40 mm) is a BS (UK) reinforcing bar to BS 4449:2005. Its nominal diameter is 40 mm, giving a cross-section area As of 1256.6 mm² and a mass of 9.864 kg/m. It is supplied in grade B500A / B500B / B500C with characteristic yield f_yk = 500 MPa. The tables below give the total steel area for 1-10 bars and the area per metre of width at common bar spacings.
| d | Nominal diameter | 40 mm |
| As | Cross-section area | 1256.6 mm² |
| m | Mass per metre | 9.864 kg/m |
| u | Nominal perimeter | 125.7 mm |
| f_yk | Characteristic yield | 500 MPa |
| Bars | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|
| As (mm²) | 1,257 | 2,513 | 3,770 | 5,026 | 6,283 | 7,540 | 8,796 | 10,053 | 11,309 | 12,566 |
| s (mm) | 75 | 100 | 125 | 150 | 175 | 200 | 250 | 300 |
|---|---|---|---|---|---|---|---|---|
| As/m (mm²/m) | 16,755 | 12,566 | 10,053 | 8,377 | 7,181 | 6,283 | 5,026 | 4,189 |
Source: BS 4449:2005. Area = π/4 × d² for metric bars; ASTM areas are the standard's tabulated nominal values. Grades available: B500A, B500B, B500C.
Understanding these values
H40 (40 mm) is a high-yield ribbed bar to BS 4449:2005, where the H prefix denotes high-yield reinforcement and the number is the diameter in millimetres. UK drawings call this bar up as H40, and it is produced to B500A / B500B / B500C with f_yk = 500 MPa. Its nominal diameter is 40 mm, which gives a cross-sectional area As of 1256.6 mm² from pi/4 times the diameter squared, and a mass of 9.864 kg/m - so a 12 m length weighs about 118.4 kg. The nominal perimeter, used in bond and anchorage calculations, is 125.7 mm.
It is supplied in B500A, B500B, B500C to BS 4449, where all three share f_yk = 500 MPa and differ only in ductility class - B500A is typically cold-worked wire for mesh, B500B is the general-purpose bar, and B500C carries the highest elongation requirement for seismic and plastic-hinge design. The grade affects the strength you design to, not the geometry: the area of 1256.6 mm² and the mass of 9.864 kg/m are the same whichever grade of BS (UK) bar is specified.
For slabs and walls the number you need is area per metre width, which is the bar area times 1,000 divided by the spacing. At 150 mm centres H40 (40 mm) gives 8377 mm²/m, at 200 mm centres 6283 mm²/m, and at 250 mm centres 5026 mm²/m. Compare those against the As,req from your slab design, take the first arrangement that satisfies it, and then check the spacing against the maximum bar spacing BS EN 1992-1-1 with the UK National Annex allows for crack control - a larger bar at wider centres can meet the area and still fail that limit.
If you are working across standards, the nearest equivalents by area are EN / Eurocode 40 mm at 1256.6 mm² (effectively identical), TCVN (Vietnam) 40 mm at 1256.6 mm² (effectively identical), ASTM (US) #14 (No. 14) at 1452 mm² (16% larger). Matching on area is the right first step, but it is not a code-sanctioned substitution: changing standard means re-checking anchorage length, lap length, bond and crack width, because those depend on bar surface geometry and the concrete, not on area alone.