How to price a slab, from the drawings to the order
The slab is the first real money on a residential job, and it is the part most often priced twice: once for the quote, again when the concreter’s price comes in and nobody can see what changed.
It is also the easiest part of an estimate to build properly, because almost everything in it comes from one measurement — the slab area — and a handful of numbers off the engineering details.
Here is the way it goes together in SmarteBuild, using the cost codes from the standard residential structure.
1. Measure it once
Open the engineer’s plan in Take-Off, set the page scale, and measure:
- The slab areas — house, garage, porch, alfresco. Keep them as separate fields rather than one lump, because the garage slab is often a different thickness and the porch is often deleted at variation stage.
- The piers — count them, and note the depth off the engineering detail.
- The strip footings — trace them as a run, in metres.
- The step downs — count them.
Each measurement becomes a named field. Nothing is typed into an item yet; you are building the numbers that the items will read.
2. Split it across four cost codes
Everything for a slab could sit under one heading called “Slab”. Do not do it. Use the four the standard structure gives you:
| Code | What belongs in it |
|---|---|
| 20-250 | Slab reinforcement — pods, mesh, bar, and their delivery |
| 20-260 | Machine hire for the slab and piers — the bobcat, the excavator |
| 20-270 | The concreter’s labour — prep and pour, piers, footings, curing |
| 20-280 | Concrete supply — the m³ from the batching plant, freight, levies |
The split is not bookkeeping for its own sake. Concrete supply and concrete placing are bought from two different businesses, and if they share a cost code you can never answer the only question that matters six weeks later: was it the concrete or the concreter that went over? Separate codes give you both numbers for free, on this job and every job after it. This is what cost codes are for.
3. Let the formulas do the arithmetic
Now the items, in the bill of quantities. Each one takes its quantity from the fields you measured, so nothing is retyped and nothing drifts.
20-250 — reinforcement. Pods and reinforcement is simply your four slab areas added together:
{House slab} + {Garage} + {Porch} + {Alfresco}priced per square metre. Underneath it sits Pods and reinforcement delivery as a flat amount, because delivery does not scale with area — it is a truck either way.
20-260 — machine hire. A bobcat allowance, usually a day rate or a lump sum. It is small and it is always forgotten, which is exactly why it deserves its own line rather than being buried in someone’s labour rate.
20-270 — the concreter. Prep and pour waffle pod slab as per engineering details reads the same four areas, at a labour rate per square metre. Then:
- Supply labour to prep and pour concrete piers —
({Piers 350} + {Piers 450}) * {Pier depth} - Supply labour to prep and pour strip footings — the footing run in metres
- Step downs — a rate each
- Curing of concrete slab — the slab areas again, at cents per square metre
Five items, one measurement behind most of them.
20-280 — concrete supply. This is where the interesting arithmetic lives, because concrete is bought in cubic metres and you measured square metres. The item converts as it goes:
({House slab} + {Garage} + {Porch} + {Alfresco}) * 0.155 + {Beam} * 0.4 * 0.4A waffle-pod slab is not a solid pour, so it does not consume its full thickness in concrete. Averaged across the area it works out near 0.155m³ per m² — that factor is doing the whole job of turning your take-off into an order quantity. The second term is the edge beam: its length times its cross-section.
The piers are the same idea with their own cross-sections:
({Piers 350} * 0.35 * 0.35 + {Piers 450} * 0.45 * 0.45) * {Pier depth}Then freight minimum charge as a fixed amount, and the environmental levy per cubic metre, which is small, real, and almost never in a spreadsheet estimate.
4. Add the waste where it belongs
Concrete gets over-ordered. Not much, but it does, and the load you send back is still paid for.
Put that on the item as a wastage percentage rather than inflating the quantity, so the measured figure stays visible and the allowance stays yours to change. If you have never measured your own, work it out from the last three jobs rather than using a round number.
5. What it gives you afterwards
Priced this way, the slab does three more things without any extra work:
The orders write themselves. Items carrying a supplier collect into a purchase order for that supplier — the batching plant gets cubic metres, the reinforcement yard gets pods and mesh, and neither quantity is retyped.
The concreter’s quote is comparable. When the price comes back, you are comparing it against your own labour lines in 20-270, not against a lump that includes materials.
The overrun shows up early. Once the invoices land, earned value reads them against those same four codes. If 20-280 is 12% over before the frame goes up, you will see it while there is still a job left to adjust.
And when the drawing changes
It will. Rev C arrives with the alfresco a metre wider.
You change the one measurement. The reinforcement, the prep and pour, the curing and the concrete supply all move with it, because every one of them reads the same field — and the volume formula does the conversion again on its own.
That is the whole argument for building a slab this way rather than typing quantities into a spreadsheet: not that it is faster the first time, but that it survives the second drawing.
Rates in the examples above come from the standard template and are there to show the shape of the estimate, not to tell you what to charge. Use your own.
SmarteBuild is Australian estimating and job management software for residential builders. Try it free for 30 days — no credit card, every module unlocked.