How to Measure Land Perimeter: Formula, Map and GPS Methods

Published November 1, 2026

The perimeter of a piece of land is the total length of its boundary: measure every side and add them up. For a rectangle that's 2 × (length + width); for an irregular lot, it's simply each side in turn. You can get the side lengths with a tape or wheel, by tapping the corners on a satellite map, or by walking the boundary with GPS.

Below are the three methods, a worked fencing example with real numbers, and the mistakes that make a perimeter come out too short or too long.

The perimeter formula for any shape of land

• Rectangle: P = 2 × (length + width). A 100 × 200 ft lot has a perimeter of 600 ft.
• Square: P = 4 × side.
• Any irregular lot: P = side 1 + side 2 + side 3 + … up to the last side.

This is the good news compared with area. To calculate the area of an irregular lot you need a diagonal or the corner positions. For perimeter, the side lengths alone are enough, however odd the shape.

The catch is the reverse: you can't work out perimeter from area alone. All three of these are one acre:

The strip needs 74% more fence than the square for exactly the same land, which is worth knowing before you buy or budget.

Three ways to measure it

1. Tape or measuring wheel

Good for small lots with clear corners and open ground. Measure each side between the actual corners, keep the tape level and tight, and write the lengths on a sketch as you go. A wheel is faster on long, smooth runs; it overreads on rough ground because it rides over every bump.

2. Tapping corners on a satellite map

Search for the address or place, zoom in fully, and tap each corner of the boundary. This is usually the quickest and most precise method when you can see the fence lines, tracks or field edges on the image. There's no walking, so it also works for land you're checking from home.

An address alone won't give you the answer, though. A map doesn't know where your boundary runs, so you have to place the corners yourself.

3. Walking the boundary with GPS

Useful when the edges aren't visible from above, for example under tree cover or on a newly cleared block. Start tracking, walk or drive the line, and finish back at the start. A phone is typically accurate to about 3–5 m (10–16 ft) under open sky and worse under trees or next to buildings, so on a small lot the map method usually wins.

Field Maps with Area Measure does the map and GPS methods on iPhone and iPad (iOS 17 or later). Perimeter and area show as you tap or walk, calculated geodesically on the WGS-84 ellipsoid, in feet, yards and miles or metres and kilometres. GPS tracking works offline, and you can save each plot under a name and come back to it. For more on the two techniques, see how to measure land area by satellite or GPS.

Worked example: from perimeter to a fencing list

A five-sided pasture has sides of 420, 310, 265, 180 and 375 ft.

• Perimeter: 420 + 310 + 265 + 180 + 375 = 1,550 ft (about 472 m)
• Subtract a 16 ft gate: 1,550 − 16 = 1,534 ft of fence line
• Posts every 10 ft: 1,534 ÷ 10 = 153.4, so round up to 154 spans. A run with an opening needs one more post than spans: 155 posts, including the two gateposts
• Three strands of wire: 1,534 × 3 = 4,602 ft
• Add 5% for ties and sag: 4,602 × 1.05 ≈ 4,832 ft
• Rolls of 1,320 ft: 4,832 ÷ 1,320 = 3.66, so 4 rolls

Treat that as a starting estimate. Corners and gate ends usually need heavier posts and bracing, and post spacing depends on the terrain, the animals and your local practice.

What makes a perimeter come out wrong

• Cutting across curves. One straight line across a bend skips length. Take a half-circle bend that's really 518 ft along the edge: one straight line reads 330 ft, adding one midpoint gives 467 ft, and three evenly spaced points give 505 ft. Add a point wherever the edge visibly changes direction.
• Walking inside the line. If you stay 3 ft inside a rectangular boundary, each side reads 6 ft short, so the total is 24 ft too low. Follow the true line, or expect the difference.
• GPS wobble. Each small drift in a recorded track adds a little length, so a walked perimeter can read long, especially at slow speed or under trees. If the corners are visible, compare it with a tapped measurement.
• Slopes. Maps give horizontal distance, while a fence follows the ground. On a steady 30% slope, 100 ft on the map is about 104 ft on the ground. On steep land, add a margin.
• Measuring to the wrong marks. An old fence isn't always on the boundary. For planning that's fine, but don't assume it's the legal line.

Handy length conversions

• 1 ft = 0.3048 m; 1 m ≈ 3.28 ft
• 1 yd = 3 ft; 1 mile = 5,280 ft = 1,760 yd
• 1,550 ft ≈ 517 yd ≈ 472 m ≈ 0.29 mile

FAQ

What is the perimeter of a piece of land?

It's the length of the full boundary, all the way around. Area tells you how much land there is; perimeter tells you how far it is around the edge, which is what matters for fencing, hedging, drainage or walking a boundary.

Can I find the perimeter if I only know the area?

Not exactly, because the shape matters. If you assume a square, the perimeter is 4 × √area, and that's the minimum for any four-sided lot. A real plot will have a longer perimeter than that.

Can I measure a property's perimeter from its address?

Partly. You can search the address on a satellite map and tap around the boundary you see, but you need to know where the corners are. The address doesn't draw the lines for you.

How many fence posts do I need?

Divide the fence length by the post spacing and round up. A closed loop needs the same number of posts as spans; a run with a gate opening needs one more. Then allow extra for corners.

Can I use this measurement for a boundary dispute?

No. A tape or phone measurement is an estimate, good for planning and budgeting. For anything legal, rely on a licensed surveyor and the recorded plat. If you only need a planning number, the Field Maps with Area Measure app is a quick way to get one.