TOC means top of concrete: the level of the finished concrete surface before any screed, topping or floor covering is added.
What TOC means
TOC means top of concrete – the level of the concrete surface at that point, as the concreter will leave it, before any screed, topping, tiles or floor covering go on.
It exists as a separate callout because concrete is rarely the surface people walk on. A slab poured to TOC RL 24.290 with a 60 mm floor build-up over it gives a finished floor at RL 24.350. Formworkers, steel fixers and surveyors work to the concrete level; tilers and joiners work to the finished level. Quoting both, and labelling which is which, is the entire point of the abbreviation.
On a footing or pile cap, TOC is the top of the pour – the level your starter bars are set from – with a separate underside or founding level below it. A column base plate is not that level: the plate underside normally sits 25 to 50 mm clear of the concrete on a grout bed, so base plate level and TOC are two different numbers on the same detail. Reading one as the other shortens or lengthens the column.
How TOC appears on a drawing
TOC prefixes a level, either absolutely or relative to another named level.
PAD FOOTING P3: TOC RL 23.150, U/S RL 22.350
COL C3 BASE: 40 GROUT BED ON TOC RL 23.150 - U/S BASE PLATE RL 23.190
SLAB ON GROUND: 150 THK, TOC RL 24.290 (= SSL)
FFL RL 24.350 - ALLOW 60 FLOOR BUILD-UP
PIT SURROUND: T.O.C. RL 24.100, FALL 1:100 TO GRATE
Same idea on a US sheet, in feet and inches:
T.O.C. EL. 100'-6"
Read those together and every gap is accounted for. The pad is 800 thick (23.150 – 22.350). The steel starts 40 above the concrete it bears on, because of the grout bed. The slab surface is 60 below the floor people walk on (24.350 – 24.290). The pit surround finishes 190 below the slab surface, out in the external paving.
Relative callouts such as TOC = FFL - 60 are convenient on repeated typical details, but they only work if the reference level is stated somewhere unambiguous on the set.
Terms TOC gets confused with
- SSL (structural slab level). For a slab, TOC and SSL usually describe the same surface, and many offices use them interchangeably. Where the slab is a burnished or polished finish left exposed, TOC, SSL and FFL all land on the same plane – and then the concreter’s surface tolerance becomes the floor tolerance, which is worth flagging early.
- FFL. Not the same as TOC unless there is no build-up. Reading one as the other is the classic way a doorway ends up with a 60 mm step nobody drew.
- Base plate level. Separated from the TOC below it by the grout bed, commonly 25 to 50 mm. Two levels, two numbers, and the steel detailer needs the plate one.
- TOS. On a composite steel floor, top of steel and top of concrete are separated by the full slab thickness measured off the top flange – deck depth plus topping, commonly 120 to 200 mm on an Australian floor.
- BOC or U/S. Bottom of concrete, or underside – the excavation and founding level, not the pour level.
- TOF (top of footing) and TOW (top of wall) – the same idea applied to specific elements. Where a set uses TOF, TOC tends to get reserved for slabs.
- Top of kerb. On civil and road drawings, particularly American ones, TOC can mean top of curb – though TC is the more common US form, paired with BC for bottom of curb and FL for flowline. Australian road sets more often use TK or TOK for the kerb and keep TOC for concrete, but that is office and authority practice, not a rule.
AU and UK versus US
The abbreviation is the same; the number after it is not. Metres to a datum in Australia and Great Britain – RL 23.150 AHD, or 23.150 AOD – against feet and inches with EL in the US, often on a project datum where the ground floor sits at EL 100′-0″.
Spelling drives the ambiguity too. Kerb in AU and UK, curb in the US, which is why TOC-as-curb is essentially an American reading – and even on a US grading plan you will meet TC far more often than TOC. Abbreviation practice sits within the AS 1100 family in Australia and ASME Y14.38 in the US. In practice it is the project’s own legend that settles what TOC means on your sheet, and offices do redefine it there.
Where to check on your own drawing set
- The abbreviations legend on the cover or general notes sheet. This is where TOC-as-concrete versus TOC-as-kerb is settled for your project.
- Structural general notes: whether slab levels are quoted as TOC/SSL or as FFL, and what floor build-up allowance has been assumed.
- Column base and holding-down bolt details, for the grout bed thickness, because that is the gap between TOC and the underside of the base plate.
- Sections and typical details, where the build-up between TOC and FFL is actually drawn rather than implied.
- The architectural finishes schedule, which tells you what thickness sits on the concrete. If it does not match the structural allowance, that is an RFI before the pour, not after.
More concrete, footing and level abbreviations are collected in the engineering drawing abbreviations list.
Other meanings of TOC
TOC collides with three things drafters meet on the same projects: Table of Contents in specifications and document registers; Total Organic Carbon on water and wastewater treatment P&IDs; and Time of Concentration in stormwater hydrology, though that is usually written as a lowercase tc. It is also Theory of Constraints in project management.