Methodology

1 · The answer is a product, not a volume

Nobody buys 2.7 cubic yards. You buy eighty-pound bags, four-by-eight sheets, boxes with a coverage printed on the side. So the calculation does not stop at the geometry: it converts to what is on the shelf, using the yield the manufacturer publishes for that exact product, and rounds up — because a second trip to the yard costs more than the spare bag.

Where the unit of sale has its own granularity, we follow it. Ready-mix is ordered in quarter-yard steps, so a 2.96 yard pour is a 3.25 yard order, and the page says so rather than reporting a number no plant will take.

2 · Waste is shown, explained and editable

The waste allowance is the part of an estimate most likely to be wrong, which is precisely why most calculators hide it inside a flat ten per cent. Here it depends on the material and on how the work is laid out — there are currently 15 allowances across 6 material groups — and each one carries the reasoning next to it.

Diagonal tile is not straight tile: every perimeter cut is on the bias and the offcut is scrap. A hallway is not an open room: each doorway starts a new row. A trench is not a slab: the walls slump and over-dig is normal. The percentage is on screen, the reason is beside it, and you can overwrite it — if you know your base is dead flat, put in five and the estimate follows you.

3 · Only labour is regionalised

This is the rule that most separates our prices from the rest, and it is the one worth arguing about. A bag of concrete mix does not cost eleven per cent more in California than in Mississippi. The hour to place it does. Sites that multiply the whole job by a single “local cost factor” inflate the material half of the estimate by a figure that mostly reflects rent.

So material and labour are computed separately. The regional index is applied to labour alone. Bulk and heavy materials carry their own freight sensitivity instead, because what moves the price of delivered concrete is the distance to the plant, not the state line — and that factor tracks the regional index at half its travel, because haulage scales less steeply than wages.

The index itself is the federal Regional Price Parities series. It is a proxy, and we say so: the direct measure would be state construction wages from the BLS occupational survey, and swapping to it is on the record in the changelog as pending.

4 · The defaults are the code, not a guess

A calculator is used by people who do not know what to type. That makes the default value the most consequential number on the page, so ours come from the standards and the trade rather than from a plausible-looking average.

Joint spacing follows the ACI guidance for slabs on ground: 2.5 times the slab thickness in inches, read as feet, cut a quarter of the depth within six to eighteen hours. Four inches is the residential section for foot traffic and cars; six with reinforcement once an RV parks on it. The bag-versus-truck crossover sits at 1 cubic yard because that is where the short-load fee overtakes the value of the concrete.

Where a default is a judgement rather than a code requirement, it is labelled as one. Where it comes from a document, the document is named on the page and listed in sources.

5 · The reader reads. The engines calculate.

The takeoff reader is the only place a language model touches this site, and it is given a deliberately small job: turn your sentence into geometry — shapes, lengths in feet, thicknesses in inches, how many. It is never asked for a quantity, a bag count or a price, and the structure it must answer in has no field to put one in.

What comes back is range-checked before it is used, and then handed to the same functions that run the calculator pages. The number you get from a description is the number you would have got by typing the dimensions in by hand, because it is literally the same code. Everything the model had to infer rather than read is listed separately, so you can disagree with the assumption instead of the answer.

What this method does not do

It does not give you a quote. It does not know your soil, your access, your inspector or what your contractor charges for a Saturday. It prices material honestly and labour approximately, and it tells you which is which — a number that admits its own tolerance is worth more than a confident one that hides it.