Blog · September 30, 2026
What Is the U.S. Survey Foot?
The U.S. survey foot is a foot definition used in many state plane coordinate systems, slightly longer than the international foot. The difference is tiny on a lot and real on a long coordinate. You do not convert it by pacing, and you do not ignore it when you move coordinates between software.
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Two feet that are almost the same
The international foot is exactly 0.3048 meters. The U.S. survey foot was defined so that one meter is 39.37 survey inches, which makes the survey foot a little longer than the international foot, by about two parts in a million. On a 100-foot lot the difference is a few thousandths of an inch, far inside a monument’s size. On a state plane coordinate in the millions of feet, using the wrong foot can shift a point by several feet. That is why the issue shows up in GIS and in survey computations, not in the width of a house lot you measure with a tape. Plats of ordinary lots are usually in feet of the era, called feet, and the foot definition is invisible until coordinates enter the conversation.
Where you will see the warning
A modern survey may state that coordinates are state plane, name the zone, the datum, and whether the foot is the U.S. survey foot. Software that assumes the international foot will place those coordinates in the wrong spot even though every number looks unchanged. The shift is a units problem, not a deed problem. It does not mean the lot moved. It means the file was interpreted in the wrong foot. County GIS layers have the same trap when they are reprojected. The parcel you see on the screen is still an assessment polygon. A foot-definition mismatch can add another offset on top of the ordinary difference between a tax map and a survey. Neither offset is something you fix by dragging a fence.
What a reader should do
If you are only reading bearings and distances in feet on a subdivision plat, you read the feet as the plat gives them. You do not apply a survey-foot factor to a 50-foot lot. If you are copying coordinates from a plat into another system, you copy the datum, the zone, and the foot definition with the numbers. If the plat is silent, do not invent a conversion. Ask the surveyor who signed it or read the local coordinate ordinance. A phone GPS reports in its own datum and will not match either foot system closely enough to reveal the difference. It is not a survey. Platbookmapper does not transform coordinates. It links to the county map, which has already chosen a projection for display.
What to do next
- On a lot plat in feet, read the distances as printed.
- On a coordinate plat, copy datum, zone, and which foot.
- Do not scale a house lot by the survey-foot factor.
- Do not use a GIS click to prove a coordinate conversion.
The mix-up to avoid
Applying a survey-foot correction to ordinary lot distances, or ignoring it when pasting state plane coordinates into software that expects the other foot. One error invents a problem. The other can move a point by feet.
Questions people ask
Did the survey foot disappear?
Federal practice has been moving to the international foot, and states have their own timelines. Existing plats and existing coordinate files still say what they used. Read the sheet in front of you rather than a national sunset date.
Will this change my deed?
No. The deed’s distances are the distances written. The foot definition matters when coordinates are the way the plat expresses those corners. Monuments on the ground still control over a coordinate that was transformed wrong.
Find the county map
Start at Platbookmapper, search the county, and open the local GIS link. Write down the parcel number before you compare the screen to a paper plat.
Not a survey. County GIS and tax parcel maps are assessment and planning layers. They are not a substitute for a recorded plat, deed, or licensed survey.