Nearly every large house-plan site offers one. Enter the plan, enter your zip code, get a number. We have chosen not to — and the reason is the most useful thing we can tell you before you buy anything.

What those tools actually do

They take the plan's square footage, apply a national cost database adjusted for your region, assume a level of finish, and return a figure. It's a model, not a quote. Nobody who produced it has seen your property.

What the model cannot see

Most of what decides your budget:

• Your lot — slope, soil, tree clearing, how far the utilities have to run, whether a truck can reach the back of the house
• Your foundation, which your site and flood zone decide, not the plan
• Your finish level, which can move the total by more than the structure costs
• Your local labor market, and how busy it is this year
• Material prices, which move faster than any database updates
• What your jurisdiction requires — engineering, elevation, energy compliance

The real danger

It isn't that the number comes out a little off. It's that the number looks precise. People budget to it, buy a plan and sometimes a lot against it, and meet the real figure months later — at the point where changing course is expensive.

What a calculator is genuinely good for

One thing, and we'll say it plainly rather than pretend otherwise: a very early, rough starting point. If you don't yet know whether you're looking at a $300,000 house or a $900,000 one, use one. Just don't budget to the output, and don't let it choose your plan.

What we would rather you did

Get the number from someone who will actually build the house. Two or three local builders, a dimensioned floor plan, a set of elevations, and your lot address. Ask for a range, not a bid.

The answers will disagree with each other, and the spread between them tells you more than any calculator output ever will.

That requires drawings in your hands, and it is the one part of this we can actually help with.

The drawings: a study set, $75

A study set is a reduced-size PDF of one plan's fully dimensioned floor plans and exterior elevations — every level of living space, all four sides, plus door and window schedules and a specification sheet covering heated area by floor, porches, garage, footprint, ceiling heights, foundation type and roof pitch.

That is enough to hand two or three builders and get a real range back. It is enough to lay on your lot and find out whether the house sits the way you pictured it.

The full $75 is credited against the construction set for that same design for twelve months. If it's the right house, the study set cost you nothing. If it isn't, you found out for $75 rather than after buying the plan — and modification quotes are free, so if it's nearly right, ask before you rule it out.

What a study set is not: buildable. There's no usable scale, no foundation plan, no framing, no sections and no electrical, and it carries no license to build. No permit office will accept one, and it isn't meant to. The construction set is what builds the house.

Study sets live on the plan they belong to. Open any plan and, where one has been drawn, you'll find it on that page. Browse the plans →

Nine things to check before you buy

What you just read is one page out of ten. The rest of the guide covers how to ask a builder for a number without wasting their time, which square footage you are actually being quoted, and the call to your building department that almost nobody makes early enough.

Written by the designer who draws the plans. A few of the checks point to us. Several don't. We left those in.