How Accurate Is a Property Survey?

A professional boundary survey is accurate to a small fraction of an inch in measurement. Under the national ALTA/NSPS Land Title Survey standard, the maximum allowable relative positional precision between adjacent corners is 2 centimeters (about 0.07 feet) plus 50 parts per million, at the 95 percent confidence level. That is far tighter than any phone GPS. But the number most people care about, "where is my line," depends less on the equipment and more on the surveyor's judgment in reconciling deeds, old monuments and boundary law, which is why two competent surveys can still differ.

How accurate is a land survey, really?

There are two separate kinds of accuracy in a survey, and mixing them up is where confusion starts. Measurement accuracy is how precisely the instruments locate a point, and with survey-grade equipment that is a fraction of an inch. Boundary accuracy is whether the corner the surveyor chose is the legally correct one, and that is a professional opinion formed from the record, the physical evidence and the law of the state. A survey can be measured perfectly and still put a corner in a defensible but debatable spot, because two surveyors can weigh conflicting old monuments differently.

What is relative positional precision?

Relative positional precision is the surveyor's estimate of how tightly the position of one boundary corner is fixed relative to the corner next to it, expressed at a 95 percent confidence level. The ALTA/NSPS standard caps it at 2 cm plus 50 ppm of the distance between the two corners. In plain terms, on a typical residential lot, adjacent corners are located relative to each other to well under an inch. When terrain, vegetation or the shape of the parcel forces a looser tolerance, the surveyor must note the reason on the plat.

How accurate is GPS for property lines?

It depends entirely on the GPS. The location dot on your phone is accurate to a few feet to several yards, which is useless for a property line where inches decide whether a fence encroaches. Survey-grade GNSS receivers, using real-time corrections, reach centimeter accuracy, and surveyors combine them with a robotic total station to tie into existing monuments. So "I checked it with GPS" means nothing without knowing which GPS. A consumer app cannot legally or practically locate your boundary, which is why having the line physically marked is the only way to get corners you can build to. If the original corners are still in the ground, our guide to finding property pins covers how to locate them first.

Can a property survey be wrong?

Yes, a survey can be wrong, and it happens for a handful of reasons: the surveyor relied on the wrong monument, misread an ambiguous old deed, made a field or math error, or was given incomplete records. A "wrong" survey is usually a boundary-interpretation problem, not a measurement one. This is exactly why a sealed survey carries the surveyor's license number and professional liability insurance behind it, and why courts have repeatedly had to weigh how the law resolves conflicting surveys when two professionals reach different conclusions on the same line.

Why do two surveys of the same property disagree?

When two surveys differ, the cause is almost always the interpretation of evidence, not the tape measure. One surveyor may hold an old iron pipe as the original corner while another gives more weight to the recorded distances, or a new subdivision plat may conflict with monuments set decades earlier. The rules of boundary law, which prioritize original monuments over later measurements, exist precisely to resolve these conflicts, but reasonable professionals can still land in slightly different places. The seal, the record research and the willingness to defend the opinion are what separate a reliable survey from a guess.

What should I do if I think my survey is wrong?

Start by asking the original surveyor to explain how they set the corner in question; often the "error" is a misunderstanding of what the plat shows. If you still disagree, hire a second licensed surveyor for an independent opinion, and give them the first survey and all your deed records. If the two professionals reach the same line, you have your answer. If they genuinely conflict, that is a boundary dispute, and it is resolved through the surveyors, the title record and, if necessary, the court, not by splitting the difference. A clear starting point is a fresh boundary survey by a licensed surveyor, and where the disagreement has already hardened into a claim, a boundary dispute survey produces the sealed plat an attorney or a court will expect.

The bottom line

A property survey done by a licensed professional is extremely accurate as a measurement and highly reliable as a legal boundary determination, but it is a professional opinion, not a machine readout. The precision is in inches or better; the judgment is what you are really paying for. If you need a boundary you can build a fence or defend a line on, get a sealed survey from a surveyor licensed in your state. Describe your project in the matcher on the Surveyors.io homepage and compare up to three quotes from verified local surveyors within about 24 hours.