Cutting a single triangle is usually done by making a square, and then cutting it in half.

There is an important measurement to remember when it comes to triangles.  It is 3/8 of an inch.

Memorize this number.  You will see this number again.  Sometimes it will have the 1/2 inch seam allowance added to it; so you will see 7/8 of an inch.

This is quite simple, but the square to the left is a 6 3/8 inch square that has been marked to be cut into a triangle.

The 3/8 inch that is added is the amount of fabric that is taken up when the triangle is added to another piece.

When you add triangles to other blocks, you will have little bits of fabric that stick out on each side.  Quilters have lots of cute names for these bits of fabric, such as bunny ears or tails.  Use your rotary cutter of scissors to trim them off.

One other thing to mention.  The triangle above is marked with a black marking pen.  However, anytime you want to mark a piece of fabric down the middle, all you need to do is fold it in half and press it.  It is a lot quicker.

This is one reason why 100% cotton is so popular with quilters.  It holds creases well.  You can even use your finger and finger press a mark that you can follow when you sew.

Triangles are usually sew together in pairs.  There are many shortcut methods.  There are only two of them that I like.  Follow the links on the left to reach those pages.