How accurate are customer supplied measurements, and what you can safely do with them

What is published on this, which is almost nothing

Search it and look at what comes back. Two ContractorTalk threads, one on customers who share measurements and one arguing about estimate accuracy in general. A meme post about a client who insisted his numbers were right and cost himself twelve thousand dollars. A homeowner facing article on whether a contractor can quote without visiting. A piece on how accurate an estimate needs to be. Then a page about quote accuracy in custom manufacturing, one on aerial roof measurements, and a legal reference page on supplied information clauses in contracts.

Two forum threads and a joke. That is the sum of what has been written for the contractor holding somebody else's numbers, and forum threads ranking high means Google has not found a better answer either.

Roofing is covered, because aerial measurement is a product. Countertops are covered, because fabricators have had this argument for twenty years. The remodeler quoting an interior from numbers a homeowner texted him is not covered at all. So here it is.

The answer is not a percentage

Everybody wants a figure. Her measurements are accurate to within five percent, say, and then you know what to do. It does not work that way, and any page that gives you a single number for this is guessing.

The useful question is not how accurate. It is accurate enough for what. And there are only two answers that matter.

Accurate enough to decide. Can you tell from her numbers whether this job is worth your Tuesday evening, and can you put a range in front of her that is honest? Almost always yes. A homeowner who measures her own kitchen will get you close enough to know whether you are looking at a refit or a gut, and close enough to say out loud that jobs like this one usually land between two figures.

Accurate enough to commit. Can you order cabinets, cut a fixed price, or buy flooring off her numbers? No. Not once, not for a good customer, not when she sounds confident. That is the line and it does not move.

The sentence your quote needs when the numbers came from her

This is the part nobody writes and it is worth more than the tolerance question. If you price off numbers somebody else supplied, say so on the document, in writing, before she signs anything.

It does two things. It keeps the conversation easy when the real measurement comes in different, because you told her in advance that it might. And it stops a price that was always a range from hardening into a promise just because it was typed neatly.

What it needs to say, in your own words: which quantities came from the customer, that the price was calculated from them, and that it is confirmed after a site measurement before any order is placed. Then make sure the site measurement actually happens on everything you win, because a clause you ignore is worse than no clause.

• Name the numbers that came from her rather than saying measurements generally.
• Say the price is subject to site verification, and say when that verification happens.
• Put it where she will read it, not in small print at the bottom.
• Have your own contract looked at by somebody who does that for a living. This is a page about measuring, not legal advice.

How to ask, so the numbers come back better

Most bad homeowner measurements are a briefing failure. She was asked for the size of the room, so she sent the size of the room. Ask differently and the numbers improve a lot.

Tell her what the number is for. Wall to wall at floor level, not at the worktop. Ceiling height taken in two places, because old houses are not level. Openings measured to the frame and the wall both. And ask her to photograph anything she is unsure about rather than guess at it, because a photograph of a thing you can identify beats a number she invented to be helpful.

Better still, stop asking her to use a tape. Text her a link instead. She opens it in her phone browser with nothing to install, and on a recent iPhone Pro the room is measured with LiDAR as she walks it. On any other phone it falls back to photographs plus the room sizes she types in, and the photos upload one at a time as she takes them so nothing is lost on a bad signal.

A vision model reads those photographs and a model writes the scope brief, and the scope is priced line by line against your own cost book. The point is not that a scan is perfect. It is that a capture she walked you through tells you what her tape never could: the condition, the obstructions, and the thing she forgot to mention.