UK structural drawings use UB (Universal Beam) and UC (Universal Column) sections, designated by serial size and weight: a 406x178x54 UB is nominally 406 mm deep, 178 mm wide, and weighs 54 kg/m. UBs are deep and narrow for bending; UCs are square-ish for axial load. The weight number in the designation is the number you take off with.
If your shop grew up on AISC callouts, the first UK drawing set you price will look familiar and read differently. The good news: British designations are actually more estimator-friendly than W-shapes, because they encode width as well as depth, and the weight is metric and exact. Here's the working reference.
What do UB and UC designations mean?
The format is depth x width x weight, all metric:
- 457x191x67 UB — serial size 457 mm deep by 191 mm wide, weighing 67 kg/m
- 203x203x46 UC — serial size 203 x 203 mm, weighing 46 kg/m
Like AISC nominal depths, the serial size is nominal: within one serial family, actual depth grows slightly with weight. A 457x191 UB family runs from 67 to 98 kg/m, and the actual depth creeps from about 453 mm to 467 mm across the range. The weight is exact and is what you multiply by length for tonnage — same discipline as reading the "x35" in a W18x35.
You'll see the same section written several ways on real drawings: "457x191x67 UB", "UB 457x191x67", "457 x 191 x 67 UB", or on older sets "457x191 UB 67". All identical — normalize before you count, the same trap covered in steel section shorthand decoded.
The rest of the UK family, briefly: PFC (Parallel Flange Channels, e.g. 230x90x32 PFC) are the channel stock, UKA angles come in equal and unequal legs, and UBP (bearing piles) look like UCs with uniform web/flange thickness. Hollow sections on UK drawings are typically Celsius (hot-finished) or Hybox (cold-formed) SHS/RHS/CHS. The definitive dimensional source is the "Blue Book" — published freely at steelconstruction.info, the SCI's resource site — and it's worth bookmarking the interactive version.
Common UB sizes chart (kg/m)
The workhorse universal beams you'll meet on most UK commercial and industrial sets. Multiply kg/m by 0.672 for lb/ft.
| Serial size | Weights available (kg/m) | Typical use |
|---|---|---|
| 127x76 UB | 13 | Trimmers, light secondary |
| 152x89 UB | 16 | Light secondary framing |
| 178x102 UB | 19 | Secondary floor beams |
| 203x133 UB | 25, 30 | Short-span floor beams |
| 254x146 UB | 31, 37, 43 | Floor beams, small roofs |
| 305x165 UB | 40, 46, 54 | The commodity floor beam |
| 356x171 UB | 45, 51, 57, 67 | Floor beams, mid spans |
| 406x178 UB | 54, 60, 67, 74 | Primary floor beams |
| 457x191 UB | 67, 74, 82, 89, 98 | Primary beams, long spans |
| 533x210 UB | 82, 92, 101, 109, 122 | Girders, transfer beams |
| 610x229 UB | 101, 113, 125, 140 | Heavy girders |
| 686x254 UB | 125, 140, 152, 170 | Long-span primary girders |
| 762x267 UB | 134, 147, 173, 197 | Very long spans |
| 838x292 UB | 176, 194, 226 | Heavy transfer work |
| 914x305 UB | 201, 224, 253, 289 | The deepest common rolled UBs |
There are narrower companions at several depths (254x102, 305x102, 305x127, 356x127, 406x140, 457x152) used where a lighter beam works — a 305x102x25 UB against a 305x165x40 UB is a 37% weight saving at the same nominal depth, and misreading the width pair on a grainy scan is a real takeoff error.
Common UC sizes chart (kg/m)
Universal columns are near-square, with flange width roughly equal to depth — the UK equivalent of the AISC W8/W10/W12/W14 column stock:
| Serial size | Weights available (kg/m) | Typical use |
|---|---|---|
| 152x152 UC | 23, 30, 37 | Light posts, small frames |
| 203x203 UC | 46, 52, 60, 71, 86 | The commodity low-rise column |
| 254x254 UC | 73, 89, 107, 132, 167 | Mid-rise columns |
| 305x305 UC | 97, 118, 137, 158, 198, 240, 283 | Heavy columns |
| 356x368 UC | 129, 153, 177, 202 | Heavy multi-storey columns |
| 356x406 UC | 235, 287, 340, 393, 467, 551, 634 | The super-heavies — column cores |
Note the pattern at the top: within one serial size, weight can vary almost 3x (305x305 runs 97 to 283 kg/m). The serial size alone tells you almost nothing about tonnage — the third number is everything. A schedule that drops the weight ("305x305 UC, see plan") forces you back to the callout, and if both are silent, RFI it rather than guess.
UCs also moonlight as beams on UK drawings more often than W14s do on American ones — shallow floor zones use UC sections as beams to save depth. Don't infer role from family.
How do UK designations differ from AISC W-shapes?
Same rolled wide-flange concept, different encoding — and the differences are exactly where cross-standard takeoffs go wrong:
| Property | AISC W-shape | UK UB/UC |
|---|---|---|
| Format | W-depth x weight (W18x35) | depth x width x weight (457x191x67 UB) |
| Units | inches, lb/ft | millimetres, kg/m |
| Width in name? | No — must look it up | Yes — second number |
| Beam vs column | One family (W) does both | Split into UB and UC families |
| Grade default | A992 (50 ksi) | S355 (or S275 on older work) |
| Reference | AISC Manual | SCI "Blue Book" |
There is no exact interchange between the families. A 305x305x97 UC sits near a W12x65; a 533x210x92 UB is in W21x62 territory — close, not equal, and substitution across standards is an engineering decision, never an estimating one. If a UK-designed job is being fabricated in North America (it happens more than you'd think), the sections are usually re-specified rather than converted. Working across designation systems is its own skill — steel takeoffs beyond AISC covers the six standards you're likely to meet, and the European sections guide handles the IPE/HEA continental families, which are different again from British UB/UC despite both being metric.
One more UK-specific habit: drawings frequently reference members through mark schedules ("B1", "C3") with the section designation living in a table on another sheet — the same schedule-key pattern covered in how to read a steel member schedule. Budget takeoff time accordingly.
What's the takeoff trap with UB and UC sections?
Three characters of the designation carry all the money:
- The weight suffix. 203x203x46 vs 203x203x86 is an 87% weight difference on an identical-looking callout. On 40 columns at 3.5 m, that's 5.6 tonnes.
- UB vs UC at similar serial sizes. A 254x254 UC and a 254x146 UB both start "254" — a truncated or smudged callout can cross families entirely.
- The narrow-width twins. 305x165 UB vs 305x127 UB vs 305x102 UB are three different beams that all read "305x1..." at low scan quality.
This is precisely the class of error automated detection plus human review is built for. SteelFlo reads full UK designations — width and weight included — from every page of an uploaded PDF and draws a bounding box around each detection, so the count you export is the count of boxes you verified on the drawing, with nothing inferred. The section library resolves 4,500+ sections across 6 standards (BS/IS, EN, AISC, AS/NZS, GB, and cold-formed SSMA) to catalog weights automatically, so a 457x191x82 UB lands in your BOM at 82 kg/m without opening the Blue Book. Combined detection plus your review runs 95–99% accuracy — and the weight suffix is exactly the one-glance detail the pairing catches best.
Quick answers
What does 406x178x54 UB mean? A Universal Beam, serial size 406 mm deep by 178 mm wide, weighing 54 kg/m. The 54 is the number you use for tonnage.
What's the difference between UB and UC? UBs are deep and narrow, optimized for bending (beams). UCs are near-square, optimized for axial load (columns). UCs also appear as beams in shallow floor zones.
How do I convert kg/m to lb/ft? Multiply by 0.672. A 305x165x40 UB is about 26.9 lb/ft — close cousin to a W12x26.
What grade is UK structural steel? S355 is today's default; S275 appears on older drawings. Check the general notes, not the member callouts.
Is there an AISC equivalent for every UB/UC? No. There are near matches (305x305x97 UC ≈ W12x65) but no exact interchanges — substitution requires engineer approval.
Pricing a UK or international set? The free steel calculator carries the full UB/UC catalog alongside AISC, EN, and AS/NZS sections — pick your sections, enter lengths, get tonnage. Browse everything at /shapes.