The easiest way to cut triangles for any quilt, is to stack up to eight layers of fabric cut to the width of the template. Then either mark the sides of the template on the top fabric with a pencil or other marking device and then lay a ruler on the lines and cut apart. Or just hold the template in place while you butt a ruler against the side of the template and carefully cut with a rotary cutter.

Freezer paper template:  You can cut some template shapes from freezer paper, and then press the shiney side to the top layer of fabric.  Then use a ruler and rotary cutter to cut around the freezer paper shapes.

There is a little waste when doing hexagons, but you will still get about 96 three inch hexagons from a stack of eight 44" wide strips. Measure patterns such as hexagons at their widest place, here it would be across the center. That would be the "width" you would use to figure your pattern size. This is "non fussy cut" of course.
 
 

	1) Figure out how many hexagons you can get from the width of the strip (usually 44" wide)  If you have a strip of fabric 44" wide and your square is 3.5. (measure your template, round up if easier) If you divide 44 by 3.5 you get 12.57. Drop the .57 and you can get 12 squares across your strip. 2) How many strips will you need?  Divide the amount of squares you need by the amount you can get from a strip. So divide 200 (amount of squares you need) by 12 (how many squares you can get across the strip) and you get 16.6 strips. Round this up to 17 strips.
3) How much fabric will you need? Take the lengh of the strips, (not the fabric) which is 3.5 in this sample, and multilpy that times how many strips you need. (This is the number you got in step two.) You need 17 strips times 3.5 (the length) and you get 59.5 inches of fabric. Round that number up to the next hole number and you need a 60 inch length of fabric. Divide 60 by 36 (one yard) and you get 1.6 yards. Of course, you will want a little more for safety so I would get 2 yards. If I really like the fabric...I will get lots more...some for the stash!
With  triangles or even half square triangles, you can get more across because you can flip flop your template. Take the widest part of the triangles, the edge that lays on the top or bottom of your strip, (measure your template and round up if necessary) and divide as usual, then multiply that by 2 because you can get double across. For the half-square triangles on the right of the illustration above, figure the measurement for the top edge of a triangle (measure your template, round up if easier) and divide that by the strip width and then multiply by 2 also, since you can get triangles on the top and the bottom.
This is a great thing to know actually. Why? Because I am a quilter that likes to use long lengthwise strips of fabric for my borders instead of piecing them. I cut my borders first on the length of the fabric and use the "leftovers" for my piecing. I can then just cut my "pieces"  from the width of the fabric I have leftover.