CRS on a drawing means centres — the centre-to-centre spacing of a repeated element, as in studs @ 450 CRS, and not the clear gap between them.
CRS on a construction drawing means centres (spelled “centers” in the US): the centre-to-centre spacing of a repeated element, measured from the centreline of one member to the centreline of the next.
It is not the clear gap. 90 x 45 STUDS @ 450 CRS leaves 405 mm of clear space between them. Set out and order off centres; measure gaps only when the note actually says CLR.
How CRS appears on a drawing
Nearly always straight after an @ and a number. A slab reinforcement note:
N12 @ 200 CRS EW BOT, 30 COVER TO SOFFIT
Read: 12 mm deformed bars at 200 mm centres, each way, in the bottom of the slab, with 30 mm cover to the underside. The cover figure is job-specific — take it from the project’s concrete notes, not from this example.
Framing and steelwork read the same way:
90 x 45 MGP10 STUDS @ 450 CRS, NOGGINGS @ 1350 MAXZ20019 PURLINS @ 1200 CRS MAXM20 8.8/S BOLTS @ 70 CRS, 35 MIN END DISTANCE
That purlin callout repays a second look. On the common Australian ranges, Z20019 is a 200 mm deep Zed with a 1.9 mm base metal thickness — the last two digits are the thickness in tenths of a millimetre, and the thickness is what governs the span. A bare “Z200” is not a designation. It cannot be ordered and it cannot be checked against a span table.
Watch for MAX and MIN. @ 600 MAX CRS is a limit, not a setting-out dimension — you may go tighter, never wider, and the real layout gets worked out to suit the length of the run.
You will also see CTS, C/C and CC for the same thing, or nothing at all: on an Australian set, STUDS @ 450 with no qualifier is normally read as centres.
Terms it gets confused with
- CRS meaning courses — masonry.
3 CRS BRICKWORK ABOVE FFLis three brick courses, not a spacing. Tell them apart by shape: courses are a small whole number with no @ in front; centres are a millimetre value following an @. - CRS meaning cold rolled steel — mostly US and Canadian shop, machining and sheet metal drawings, and it turns up in a material note rather than a spacing:
MATL: 3 mm CRS. It never follows an @. - CTS, C/C, O.C. — identical meaning, different office habits.
- CL and the centreline symbol — a single line to set out from, not a repeat spacing.
- CLR / CLEAR — the gap between faces. The other end of the same dimension chain.
- PITCH and GAUGE — in steel detailing, bolt spacing along a member and across it. Both are centres; the words carry the direction.
AU/UK versus US
- AU, NZ, UK — CRS and CTS are both normal, spelled with the British “-re”, in millimetres with no units shown.
- US —
O.C.is the standard form:2x4 STUDS @ 16" O.C.CRS in the spacing sense is unusual there, and a US fabricator will very likely read it as cold rolled steel.
If a set is going offshore for fabrication or detailing, define CRS in the legend or just write “centres” out in full. It is a five-second fix that removes a whole class of RFI.
Where to check on your own set
- The abbreviation legend and the structural general notes.
- Typical details and sections — confirm the dimension lines actually land on centrelines and not on faces.
- The reinforcement or bar bending schedule, which governs over plan notes in most offices.
- Span tables. For timber framing, member size and spacing are linked through AS 1684; for purlins and battens, through the manufacturer’s tables for that exact section and thickness. If the drawing spacing conflicts with the table, ask before you build.
- Any note where CRS appears without an @ and with a small number — read it as courses and confirm.
CRS sits with the rest of the spacing and dimension shorthand in the A-Z of engineering drawing abbreviations.
Other meanings of CRS
Outside drafting, CRS is the Common Reporting Standard (international tax reporting), the Congressional Research Service (US), and Child Restraint System (vehicle seats). Within drafting it genuinely collides with two other readings — courses in masonry, and cold rolled steel on US shop drawings — both covered above.