RSJ
Rolled Steel Joist, the pre-1970s tapered-flange profile. The name stuck, the section didn't: ask a merchant for an RSJ today and you'll be handed a universal beam. Only heritage repair work still calls for true RSJ profiles.
Steelwork reference
UK Steel Beam Sizes: UB, UC and RSJ
Every standard UK beam size in one place: 107 universal beams, 46 universal columns and 16 channels, with depth, width, thickness and weight per metre from the published UK section tables. Plus what people actually mean by RSJ sizes.
How UK beam sizes work
A size like 203 x 133 x 25 UB reads: nominal depth 203 mm, nominal flange width 133 mm, weight 25 kg per metre. UB is the standard UK I-beam (what most people call an RSJ), UC is the squarer column profile, and PFC is the C-shaped channel.
Universal beam (UB) sizes: the RSJ chart
All 107 standard UB sizes, from 127 x 76 x 13 to 1016 x 305 x 584, smallest first. Depth and width are the measured figures for each weight, not the nominal serial size. Ix is the second moment of area and Zx the elastic section modulus, the two numbers that decide stiffness and bending strength.
| Designation | Mass (kg/m) | Depth (mm) | Width (mm) | Web (mm) | Flange (mm) | Ix (cm⁴) | Zx (cm³) |
|---|---|---|---|---|---|---|---|
| 127 x 76 x 13 UB | 13 | 127 | 76 | 4 | 7.6 | 473 | 74.6 |
| 152 x 89 x 16 UB | 16 | 152.4 | 88.7 | 4.5 | 7.7 | 834 | 109 |
| 178 x 102 x 19 UB | 19 | 177.8 | 101.2 | 4.8 | 7.9 | 1360 | 153 |
| 203 x 102 x 23 UB | 23.1 | 203.2 | 101.8 | 5.4 | 9.3 | 2100 | 207 |
| 203 x 133 x 25 UB | 25.1 | 203.2 | 133.2 | 5.7 | 7.8 | 2340 | 230 |
| 203 x 133 x 30 UB | 30 | 206.8 | 133.9 | 6.4 | 9.6 | 2900 | 280 |
| 254 x 102 x 22 UB | 22 | 254 | 101.6 | 5.7 | 6.8 | 2840 | 224 |
| 254 x 102 x 25 UB | 25.2 | 257.2 | 101.9 | 6 | 8.4 | 3410 | 266 |
| 254 x 102 x 28 UB | 28.3 | 260.4 | 102.2 | 6.3 | 10 | 4000 | 308 |
| 254 x 146 x 31 UB | 31.1 | 251.4 | 146.1 | 6 | 8.6 | 4410 | 351 |
| 254 x 146 x 37 UB | 37 | 256 | 146.4 | 6.3 | 10.9 | 5540 | 433 |
| 254 x 146 x 43 UB | 43 | 259.6 | 147.3 | 7.2 | 12.7 | 6540 | 504 |
| 305 x 102 x 25 UB | 24.8 | 305.1 | 101.6 | 5.8 | 7 | 4460 | 292 |
| 305 x 102 x 28 UB | 28.2 | 308.7 | 101.8 | 6 | 8.8 | 5370 | 348 |
| 305 x 102 x 33 UB | 32.8 | 312.7 | 102.4 | 6.6 | 10.8 | 6500 | 416 |
| 305 x 127 x 37 UB | 37 | 304.4 | 123.4 | 7.1 | 10.7 | 7170 | 471 |
| 305 x 127 x 42 UB | 41.9 | 307.2 | 124.3 | 8 | 12.1 | 8200 | 534 |
| 305 x 127 x 48 UB | 48.1 | 311 | 125.3 | 9 | 14 | 9570 | 616 |
| 305 x 165 x 40 UB | 40.3 | 303.4 | 165 | 6 | 10.2 | 8500 | 560 |
| 305 x 165 x 46 UB | 46.1 | 306.6 | 165.7 | 6.7 | 11.8 | 9900 | 646 |
| 305 x 165 x 54 UB | 54 | 310.4 | 166.9 | 7.9 | 13.7 | 11700 | 754 |
| 356 x 127 x 33 UB | 33.1 | 349 | 125.4 | 6 | 8.5 | 8250 | 473 |
| 356 x 127 x 39 UB | 39.1 | 353.4 | 126 | 6.6 | 10.7 | 10200 | 576 |
| 356 x 171 x 45 UB | 45 | 351.4 | 171.1 | 7 | 9.7 | 12100 | 687 |
| 356 x 171 x 51 UB | 51 | 355 | 171.5 | 7.4 | 11.5 | 14100 | 796 |
| 356 x 171 x 57 UB | 57 | 358 | 172.2 | 8.1 | 13 | 16000 | 896 |
| 356 x 171 x 67 UB | 67.1 | 363.4 | 173.2 | 9.1 | 15.7 | 19500 | 1070 |
| 406 x 140 x 39 UB | 39 | 398 | 141.8 | 6.4 | 8.6 | 12500 | 629 |
| 406 x 140 x 46 UB | 46 | 403.2 | 142.2 | 6.8 | 11.2 | 15700 | 778 |
| 406 x 140 x 53 UB | 53.3 | 406.6 | 143.3 | 7.9 | 12.9 | 18300 | 899 |
| 406 x 178 x 54 UB | 54.1 | 402.6 | 177.7 | 7.7 | 10.9 | 18700 | 930 |
| 406 x 178 x 60 UB | 60.1 | 406.4 | 177.9 | 7.9 | 12.8 | 21600 | 1060 |
| 406 x 178 x 67 UB | 67.1 | 409.4 | 178.8 | 8.8 | 14.3 | 24300 | 1190 |
| 406 x 178 x 74 UB | 74.2 | 412.8 | 179.5 | 9.5 | 16 | 27300 | 1320 |
| 406 x 178 x 85 UB | 85.3 | 417.2 | 181.9 | 10.9 | 18.2 | 31700 | 1520 |
| 457 x 152 x 52 UB | 52.3 | 449.8 | 152.4 | 7.6 | 10.9 | 21400 | 950 |
| 457 x 152 x 60 UB | 59.8 | 454.6 | 152.9 | 8.1 | 13.3 | 25500 | 1120 |
| 457 x 152 x 67 UB | 67.2 | 458 | 153.8 | 9 | 15 | 28900 | 1260 |
| 457 x 152 x 74 UB | 74.2 | 462 | 154.4 | 9.6 | 17 | 32700 | 1410 |
| 457 x 152 x 82 UB | 82.1 | 465.8 | 155.3 | 10.5 | 18.9 | 36600 | 1570 |
| 457 x 191 x 67 UB | 67.1 | 453.4 | 189.9 | 8.5 | 12.7 | 29400 | 1300 |
| 457 x 191 x 74 UB | 74.3 | 457 | 190.4 | 9 | 14.5 | 33300 | 1460 |
| 457 x 191 x 82 UB | 82 | 460 | 191.3 | 9.9 | 16 | 37100 | 1610 |
| 457 x 191 x 89 UB | 89.3 | 463.4 | 191.9 | 10.5 | 17.7 | 41000 | 1770 |
| 457 x 191 x 98 UB | 98.3 | 467.2 | 192.8 | 11.4 | 19.6 | 45700 | 1960 |
| 457 x 191 x 106 UB | 105.8 | 469.2 | 194 | 12.6 | 20.6 | 48900 | 2080 |
| 457 x 191 x 133 UB | 133.3 | 480.6 | 196.7 | 15.3 | 26.3 | 63800 | 2660 |
| 457 x 191 x 161 UB | 161.4 | 492 | 199.4 | 18 | 32 | 79800 | 3240 |
| 533 x 165 x 66 UB | 65.7 | 524.7 | 165.1 | 8.9 | 11.4 | 35000 | 1340 |
| 533 x 165 x 75 UB | 74.7 | 529.1 | 165.9 | 9.7 | 13.6 | 41100 | 1550 |
| 533 x 165 x 85 UB | 84.8 | 534.9 | 166.5 | 10.3 | 16.5 | 48500 | 1820 |
| 533 x 210 x 82 UB | 82.2 | 528.3 | 208.8 | 9.6 | 13.2 | 47500 | 1800 |
| 533 x 210 x 92 UB | 92.1 | 533.1 | 209.3 | 10.1 | 15.6 | 55200 | 2070 |
| 533 x 210 x 101 UB | 101 | 536.7 | 210 | 10.8 | 17.4 | 61500 | 2290 |
| 533 x 210 x 109 UB | 109 | 539.5 | 210.8 | 11.6 | 18.8 | 66800 | 2480 |
| 533 x 210 x 122 UB | 122 | 544.5 | 211.9 | 12.7 | 21.3 | 76000 | 2790 |
| 533 x 210 x 138 UB | 138.3 | 549.1 | 213.9 | 14.7 | 23.6 | 86100 | 3140 |
| 533 x 312 x 151 UB | 150.6 | 542.5 | 312 | 12.7 | 20.3 | 101000 | 3710 |
| 533 x 312 x 182 UB | 181.5 | 550.7 | 314.5 | 15.2 | 24.4 | 123000 | 4480 |
| 533 x 312 x 219 UB | 218.8 | 560.3 | 317.4 | 18.3 | 29.2 | 151000 | 5400 |
| 533 x 312 x 273 UB | 273.3 | 577.1 | 320.2 | 21.1 | 37.6 | 199000 | 6890 |
| 610 x 178 x 82 UB | 81.8 | 598.6 | 177.9 | 10 | 12.8 | 55900 | 1870 |
| 610 x 178 x 92 UB | 92.2 | 603 | 178.8 | 10.9 | 15 | 64600 | 2140 |
| 610 x 178 x 100 UB | 100.3 | 607.4 | 179.2 | 11.3 | 17.2 | 72500 | 2390 |
| 610 x 229 x 101 UB | 101.2 | 602.6 | 227.6 | 10.5 | 14.8 | 75800 | 2520 |
| 610 x 229 x 113 UB | 113 | 607.6 | 228.2 | 11.1 | 17.3 | 87300 | 2870 |
| 610 x 229 x 125 UB | 125.1 | 612.2 | 229 | 11.9 | 19.6 | 98600 | 3220 |
| 610 x 229 x 140 UB | 139.9 | 617.2 | 230.2 | 13.1 | 22.1 | 112000 | 3620 |
| 610 x 305 x 149 UB | 149.2 | 612.4 | 304.8 | 11.8 | 19.7 | 126000 | 4110 |
| 610 x 305 x 179 UB | 179 | 620.2 | 307.1 | 14.1 | 23.6 | 153000 | 4930 |
| 610 x 305 x 238 UB | 238.1 | 635.8 | 311.4 | 18.4 | 31.4 | 209000 | 6590 |
| 686 x 254 x 125 UB | 125.2 | 677.9 | 253 | 11.7 | 16.2 | 118000 | 3480 |
| 686 x 254 x 140 UB | 140.1 | 683.5 | 253.7 | 12.4 | 19 | 136000 | 3990 |
| 686 x 254 x 152 UB | 152.4 | 687.5 | 254.5 | 13.2 | 21 | 150000 | 4370 |
| 686 x 254 x 170 UB | 170.2 | 692.9 | 255.8 | 14.5 | 23.7 | 170000 | 4920 |
| 762 x 267 x 134 UB | 133.9 | 750 | 264.4 | 12 | 15.5 | 151000 | 4020 |
| 762 x 267 x 147 UB | 146.9 | 754 | 265.2 | 12.8 | 17.5 | 169000 | 4470 |
| 762 x 267 x 173 UB | 173 | 762.2 | 266.7 | 14.3 | 21.6 | 205000 | 5390 |
| 762 x 267 x 197 UB | 196.8 | 769.8 | 268 | 15.6 | 25.4 | 240000 | 6230 |
| 838 x 292 x 176 UB | 175.9 | 834.9 | 291.7 | 14 | 18.8 | 246000 | 5890 |
| 838 x 292 x 194 UB | 193.8 | 840.7 | 292.4 | 14.7 | 21.7 | 279000 | 6640 |
| 838 x 292 x 226 UB | 226.5 | 850.9 | 293.8 | 16.1 | 26.8 | 340000 | 7980 |
| 914 x 305 x 201 UB | 200.9 | 903 | 303.3 | 15.1 | 20.2 | 325000 | 7200 |
| 914 x 305 x 224 UB | 224.2 | 910.4 | 304.1 | 15.9 | 23.9 | 376000 | 8270 |
| 914 x 305 x 238 UB | 238 | 915 | 305 | 16.5 | 25.9 | 406000 | 8880 |
| 914 x 305 x 253 UB | 253.4 | 918.4 | 305.5 | 17.3 | 27.9 | 436000 | 9500 |
| 914 x 305 x 271 UB | 271 | 923 | 307 | 18.4 | 30 | 472000 | 10200 |
| 914 x 305 x 289 UB | 289.1 | 926.6 | 307.7 | 19.5 | 32 | 504000 | 10900 |
| 914 x 305 x 313 UB | 313 | 932 | 309 | 21.1 | 34.5 | 548000 | 11800 |
| 914 x 305 x 345 UB | 345 | 943 | 308 | 22.1 | 39.9 | 626000 | 13300 |
| 914 x 305 x 381 UB | 381 | 951 | 310 | 24.4 | 43.9 | 697000 | 14600 |
| 914 x 305 x 425 UB | 425 | 961 | 313 | 26.9 | 49 | 788000 | 16400 |
| 914 x 305 x 474 UB | 474 | 971 | 316 | 30 | 54.1 | 886000 | 18200 |
| 914 x 305 x 521 UB | 521 | 981 | 319 | 33 | 58.9 | 982000 | 20000 |
| 914 x 305 x 576 UB | 576 | 993 | 322 | 36.1 | 65 | 1102000 | 22200 |
| 914 x 419 x 343 UB | 343.3 | 911.8 | 418.5 | 19.4 | 32 | 626000 | 13700 |
| 914 x 419 x 388 UB | 388 | 921 | 420.5 | 21.4 | 36.6 | 720000 | 15600 |
| 1016 x 305 x 222 UB | 222 | 970.3 | 300 | 16 | 21.1 | 408000 | 8410 |
| 1016 x 305 x 249 UB | 248.7 | 980.1 | 300 | 16.5 | 26 | 481000 | 9820 |
| 1016 x 305 x 272 UB | 272.3 | 990.1 | 300 | 16.5 | 31 | 554000 | 11200 |
| 1016 x 305 x 314 UB | 314.3 | 999.9 | 300 | 19.1 | 35.9 | 644000 | 12900 |
| 1016 x 305 x 350 UB | 350 | 1008 | 302 | 21.1 | 40 | 723000 | 14300 |
| 1016 x 305 x 393 UB | 392.7 | 1015.9 | 303 | 24.4 | 43.9 | 808000 | 15900 |
| 1016 x 305 x 415 UB | 415 | 1020 | 304 | 26 | 46 | 853000 | 16700 |
| 1016 x 305 x 438 UB | 438 | 1026 | 305 | 26.9 | 49 | 910000 | 17700 |
| 1016 x 305 x 494 UB | 494 | 1036 | 309 | 31 | 54 | 1028000 | 19800 |
| 1016 x 305 x 584 UB | 584 | 1056 | 314 | 36 | 64 | 1246000 | 23600 |
Data from the published UK section tables. Always confirm section availability with your steel stockholder before detailing.
Universal column (UC) sizes
All 46 standard UC sizes. Squarer than a UB, so they suit tight headroom and double duty as columns. When someone asks for a 6 inch RSJ, a 152 x 152 UC is often what they end up with.
| Designation | Mass (kg/m) | Depth (mm) | Width (mm) | Web (mm) | Flange (mm) | Ix (cm⁴) | Zx (cm³) |
|---|---|---|---|---|---|---|---|
| 152 x 152 x 23 UC | 23 | 152.4 | 152.2 | 5.8 | 6.8 | 1250 | 164 |
| 152 x 152 x 30 UC | 30 | 157.6 | 152.9 | 6.5 | 9.4 | 1750 | 222 |
| 152 x 152 x 37 UC | 37 | 161.8 | 154.4 | 8 | 11.5 | 2210 | 273 |
| 152 x 152 x 44 UC | 44 | 166 | 155.9 | 9.5 | 13.6 | 2700 | 326 |
| 152 x 152 x 51 UC | 51.2 | 170.2 | 157.4 | 11 | 15.7 | 3230 | 379 |
| 203 x 203 x 46 UC | 46.1 | 203.2 | 203.6 | 7.2 | 11 | 4570 | 450 |
| 203 x 203 x 52 UC | 52 | 206.2 | 204.3 | 7.9 | 12.5 | 5260 | 510 |
| 203 x 203 x 60 UC | 60 | 209.6 | 205.8 | 9.4 | 14.2 | 6120 | 584 |
| 203 x 203 x 71 UC | 71 | 215.8 | 206.4 | 10 | 17.3 | 7620 | 706 |
| 203 x 203 x 86 UC | 86.1 | 222.2 | 209.1 | 12.7 | 20.5 | 9450 | 850 |
| 203 x 203 x 100 UC | 99.6 | 228.6 | 210.3 | 14.5 | 23.7 | 11300 | 988 |
| 203 x 203 x 113 UC | 113.5 | 235 | 212.1 | 16.3 | 26.9 | 13300 | 1130 |
| 203 x 203 x 127 UC | 127.5 | 241.4 | 213.9 | 18.1 | 30.1 | 15400 | 1280 |
| 254 x 254 x 73 UC | 73.1 | 254.1 | 254.6 | 8.6 | 14.2 | 11400 | 898 |
| 254 x 254 x 89 UC | 88.9 | 260.3 | 256.3 | 10.3 | 17.3 | 14300 | 1100 |
| 254 x 254 x 107 UC | 107.1 | 266.7 | 258.8 | 12.8 | 20.5 | 17500 | 1310 |
| 254 x 254 x 132 UC | 132 | 276.3 | 261.3 | 15.3 | 25.3 | 22500 | 1630 |
| 254 x 254 x 167 UC | 167.1 | 289.1 | 265.2 | 19.2 | 31.7 | 30000 | 2080 |
| 305 x 305 x 97 UC | 96.9 | 307.9 | 305.3 | 9.9 | 15.4 | 22200 | 1450 |
| 305 x 305 x 118 UC | 117.9 | 314.5 | 307.4 | 12 | 18.7 | 27700 | 1760 |
| 305 x 305 x 137 UC | 136.9 | 320.5 | 309.2 | 13.8 | 21.7 | 32800 | 2050 |
| 305 x 305 x 158 UC | 158.1 | 327.1 | 311.2 | 15.8 | 25 | 38700 | 2370 |
| 305 x 305 x 198 UC | 198.1 | 339.9 | 314.5 | 19.1 | 31.4 | 50900 | 3000 |
| 305 x 305 x 240 UC | 240 | 352.5 | 318.4 | 23 | 37.7 | 64200 | 3640 |
| 305 x 305 x 283 UC | 282.9 | 365.3 | 322.2 | 26.8 | 44.1 | 78900 | 4320 |
| 356 x 368 x 129 UC | 129 | 355.6 | 368.6 | 10.4 | 17.5 | 40200 | 2260 |
| 356 x 368 x 153 UC | 152.9 | 362 | 370.5 | 12.3 | 20.7 | 48600 | 2680 |
| 356 x 368 x 177 UC | 177 | 368.2 | 372.6 | 14.4 | 23.8 | 57100 | 3100 |
| 356 x 368 x 202 UC | 201.9 | 374.6 | 374.7 | 16.5 | 27 | 66300 | 3540 |
| 356 x 406 x 235 UC | 235.1 | 381 | 394.8 | 18.4 | 30.2 | 79100 | 4150 |
| 356 x 406 x 287 UC | 287.1 | 393.6 | 399 | 22.6 | 36.5 | 99900 | 5070 |
| 356 x 406 x 340 UC | 339.9 | 406.4 | 403 | 26.6 | 42.9 | 123000 | 6030 |
| 356 x 406 x 393 UC | 393 | 419 | 407 | 30.6 | 49.2 | 147000 | 7000 |
| 356 x 406 x 467 UC | 467 | 436.6 | 412.2 | 35.8 | 58 | 183000 | 8380 |
| 356 x 406 x 509 UC | 509 | 446 | 416 | 39.1 | 62.7 | 204000 | 9170 |
| 356 x 406 x 551 UC | 551 | 455.6 | 418.5 | 42.1 | 67.5 | 227000 | 9960 |
| 356 x 406 x 592 UC | 592 | 465 | 421 | 45 | 72.3 | 250000 | 10800 |
| 356 x 406 x 634 UC | 633.9 | 474.6 | 424 | 47.6 | 77 | 275000 | 11600 |
| 356 x 406 x 677 UC | 677 | 483 | 428 | 51.2 | 81.5 | 300000 | 12400 |
| 356 x 406 x 744 UC | 744 | 498 | 432 | 55.6 | 88.9 | 342000 | 13700 |
| 356 x 406 x 818 UC | 818 | 514 | 437 | 60.5 | 97 | 392000 | 15300 |
| 356 x 406 x 900 UC | 900 | 531 | 442 | 65.9 | 106 | 450000 | 17000 |
| 356 x 406 x 990 UC | 990 | 550 | 448 | 71.9 | 115 | 519000 | 18900 |
| 356 x 406 x 1086 UC | 1086 | 569 | 454 | 78 | 125 | 596000 | 20900 |
| 356 x 406 x 1202 UC | 1202 | 580 | 471 | 95 | 130 | 664000 | 22900 |
| 356 x 406 x 1299 UC | 1299 | 600 | 476 | 100 | 140 | 755000 | 25200 |
Parallel flange channel (PFC) sizes
All 16 standard PFC sizes. Channels turn up as trimmers, lintel partners and framing where one flat face makes fixing easier.
| Designation | Mass (kg/m) | Depth (mm) | Width (mm) | Web (mm) | Flange (mm) | Ix (cm⁴) | Zx (cm³) |
|---|---|---|---|---|---|---|---|
| 100 x 50 x 10 PFC | 10.2 | 100 | 50 | 5 | 8.5 | 208 | 41.5 |
| 125 x 65 x 15 PFC | 14.8 | 125 | 65 | 5.5 | 9.5 | 483 | 77.3 |
| 150 x 75 x 18 PFC | 17.9 | 150 | 75 | 5.5 | 10 | 861 | 115 |
| 150 x 90 x 24 PFC | 23.9 | 150 | 90 | 6.5 | 12 | 1160 | 155 |
| 180 x 75 x 20 PFC | 20.3 | 180 | 75 | 6 | 10.5 | 1370 | 152 |
| 180 x 90 x 26 PFC | 26.1 | 180 | 90 | 6.5 | 12.5 | 1820 | 202 |
| 200 x 75 x 23 PFC | 23.4 | 200 | 75 | 6 | 12.5 | 1960 | 196 |
| 200 x 90 x 30 PFC | 29.7 | 200 | 90 | 7 | 14 | 2520 | 252 |
| 230 x 75 x 26 PFC | 25.7 | 230 | 75 | 6.5 | 12.5 | 2750 | 239 |
| 230 x 90 x 32 PFC | 32.2 | 230 | 90 | 7.5 | 14 | 3520 | 306 |
| 260 x 75 x 28 PFC | 27.6 | 260 | 75 | 7 | 12 | 3620 | 278 |
| 260 x 90 x 35 PFC | 34.8 | 260 | 90 | 8 | 14 | 4730 | 364 |
| 300 x 90 x 41 PFC | 41.4 | 300 | 90 | 9 | 15.5 | 7220 | 481 |
| 300 x 100 x 46 PFC | 45.5 | 300 | 100 | 9 | 16.5 | 8230 | 549 |
| 380 x 100 x 54 PFC | 54 | 380 | 100 | 9.5 | 17.5 | 15000 | 791 |
| 430 x 100 x 64 PFC | 64.4 | 430 | 100 | 11 | 19 | 21900 | 1020 |
How far can a steel beam span? Read this before the chart
There is no honest span chart that works without knowing the load. What the trade actually uses at planning stage is a depth habit: floor beams tend to land around a fifteenth to an eighteenth of the span deep, and lightly loaded roof members can stretch further. So a 4 m span points at something roughly 230 to 270 mm deep, and a 6 m span at 330 to 400 mm. That narrows the chart down; it never confirms a beam.
From there, run the real numbers: put your span, load and candidate section into the free steel beam calculator and it checks bending, shear and deflection against planning guides in seconds. The final size is always the structural engineer's call.
RSJ, UB, UC: what people actually mean
Three names that cause more confusion on site than any other bit of steel vocabulary.
UB, universal beam
The modern UK I-beam with parallel flanges, rolled in 107 standard sizes. Deep for its weight, so it's the default choice where bending governs: floor beams, roof beams, trimmers, goalposts.
UC, universal column
Roughly square, made to take load along its length as a column, but regularly used as a shallow beam where every millimetre of headroom counts, a loft conversion favourite.
Sizes FAQ
Quick answers on beam sizes, RSJ names and spans
The questions that come up when someone is staring at a size chart trying to turn it into an order.
What sizes do UK steel beams come in?
UK universal beams (UB) run from 127 x 76 x 13 up to 1016 x 305 x 584, in 107 standard sizes. Universal columns (UC) run from 152 x 152 x 23 up to 356 x 406 x 634 in 46 sizes, and parallel flange channels (PFC) from 100 x 50 x 10 to 430 x 100 x 64. The full dimension and weight charts for every size are on this page.
How do I read a steel beam size like 203 x 133 x 25?
The first number is the nominal depth in millimetres, the second is the nominal flange width, and the third is the weight in kilograms per metre. So a 203 x 133 x 25 UB is roughly 203 mm deep, 133 mm wide, and weighs 25 kg for every metre of length. The exact depth and width vary slightly between weights in the same serial size, which is why the charts list the precise figures.
What are standard RSJ sizes?
RSJ (rolled steel joist) is the old name people still use for a steel beam, but the sections actually rolled and sold in the UK today are universal beams (UB) and universal columns (UC). When a builder or merchant talks about a 6 inch or 8 inch RSJ, they usually mean a 152 or 203 series UB or UC. So the RSJ size chart you're after is the UB and UC charts on this page.
Are RSJ and UB the same thing?
In everyday use, yes. True tapered-flange RSJs are an older profile that has almost entirely been replaced by parallel-flange universal beams. Unless you're matching steel in a heritage building, an RSJ on a modern job means a UB or UC.
What size steel beam do I need for my span?
It depends on the load, not just the span, so no honest chart can answer that on its own. As a very rough planning habit, floor beams often end up with a depth around a fifteenth to an eighteenth of the span, so a 4 m span suggests something in the 230 to 270 mm deep range as a starting guess. Check the actual numbers with the free Fabora steel beam calculator, then have the final size confirmed by a structural engineer. The calculator is a planning tool, not approval.
Which is the lightest and heaviest UK universal beam?
The lightest UB is the 127 x 76 x 13 at 13 kg/m, and the heaviest is the 1016 x 305 x 584 at 584 kg/m. In total there are 107 standard UB sizes.
Is UC or UB better for a beam?
UBs are deeper for their weight, so they carry bending loads more efficiently and are the usual choice for a beam. UCs are squarer, which makes them the pick when headroom is tight and a shallower, wider section is worth the extra weight, or when the member also works as a column. Run both through the beam calculator and compare.