Situation 1 – When you know the finished length of the long side of a triangle, multiply that number by .707 to get the length of the short sides. Then, add 7/8″ (0.875) to each side for seam allowances.

Example:  I want a triangle where the long side, when sewn, will measure 2″.

Multiply 2.00 x .707 =  1.414 inches
To this total,  add 7/8″ or 0.875
1.414 inches  +  0.875 inches  =  2.29 inches

I will cut a square  2.29 inches on each side, and cut it diagonally IN ONE DIRECTION to make triangles  that, when sewn,  will measure 2 inches on the long side.

Situation 2 – When you know the finished length of the short side of the triangle, multiply that number by 1.414 to get the length of the long sides. Then, add 1-1/4″ (1.25) to each side for seam allowances.

Example:  I want a triangle where each short side, when sewn, will measure 2″.

Multiply 2.00 x 1.414 =  2.828 inches
To this total,  add 1-1/4″ or 1.25
2.828 inches +  1.25 inches  =  4.08 inches

I will cut a square 4.08 inches on each side, and cut it diagonally in BOTH DIRECTIONS to make triangles that, when sewn,  will measure 2 inches on each side.