Construction Estimating
A price is a quantity multiplied by a rate, and almost every argument about cost is really an argument about the quantity.
The calculators
The rest of this site calculates quantities: boards, cubic yards, linear feet, fasteners. This section is about the other half, and about the one number that gets quoted more than any other and survives the least scrutiny.
Cost per square foot is a ratio, and its denominator is undefined. Builders divide by heated area, by area under roof, or by footprint, according to habit rather than convention, and on an ordinary two storey house with a garage those three numbers span twenty percent. Two builders can quote the same job, state different rates, mean the same money, and neither has said a wrong thing. The useful question in that conversation is not what the rate is, it is what it was divided by.
Most of a building is priced by the foot, not the square foot. Footings, foundation walls, sill plates, exterior framing, sheathing, housewrap, siding, corner boards, soffit, fascia, gutters, roof edge and flashing all scale with perimeter. Flooring, drywall, ceilings, insulation and roof covering scale with area. A long thin house buys more of the first group for the same amount of the second, and no rate card carries a shape adjustment.
Why there are no prices on this site
This site publishes no cost figure of its own, anywhere. Where a page needs a price to be useful it quotes somebody else's, with a byline and a date, and says whose it is. Cost per square foot is the figure where publishing our own would be least defensible: the numerator moves with specification, labour market and season, and the denominator is not even agreed.
What a calculator can honestly do instead is show the quantity the rate is standing in for. That is a number that does not go stale, does not vary by region, and is the thing you would have to argue about if you wanted to argue with a quote.
What belongs here
This section holds the cross-trade cost method: how areas are defined, what drives cost that floor area does not capture, and how to read a rate somebody hands you. Trade-specific quantities live with their trade, and the cost pages in each trade hub pre-fill from sourced third-party ranges rather than from anything invented here.