How to Make a Perfect Right Angle on a Fence

If you are installing a fence to enclose a square area, you want the corners to form 90 degree angles. An effective method of plotting a perfect right angle on a fence is the 3-4-5 triangle method. This involves placing tape measures at the 3-foot, 4-foot and 5-foot marks, creating a triangle. Allow two to three hours for plotting the right angle of your fence. You need basic math and landscaping skills to complete this task.

Plan your right angle before installing a fence.
  • Mark the fence line with stakes and mason's string. Place a stake on the outside of the corner with a hammer and connect the corner stakes to the previous stakes with mason's string. Place another stake 3 feet out from the corner stake along the line, using a hammer.

  • Mark the adjacent side by positioning the end of a tape measure at the outside corner stake and out along the adjacent, connecting side. Open the tape measure to extend beyond the 4-foot mark and lock it in place, pressing the lock button.

  • Position the end of a different tape measure at the 3-foot stake on the first side and open it past the 5-foot mark. Lock it in place.

  • Angle the second tape measure toward the first, intersecting them at the 5-foot mark. This gives you the diagonal measurement. Angle the second tape measure while it's still intersected at the 4-foot mark for the perpendicular measurement.

  • Run a mason's string from the stake the two tape measures are at to the outside corner stake. The 3-foot and 4-foot mason's string forms the right angle for the fence. Extend or shorten the mason's string if needed.

  • Stake out the exact dimensions for the rest of the fence according to your map.

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