I too do this and cut down if I need to.

Just be sure the 45degreen on you ruler follows the diagonal line and hits the point at the end.

If you use the wonder cut ruler you will have it perfect every time and save fabric too.

I also round up to the nearest inch - I don't mind the extra stepin trimming because I know I'll be able to use EVERY HST I make - unlike with the 7/8 margin. The ruler or rotary cutter can shift slightly during cutting without my being able to notice, so that extra 1/8" is good insurance to have.

I add 1" and trim them down. More laborious but better HSTs.

Round up, and even add another 1/4-1/2" if you have to. You are only cutting off smidgeons so to me it isn't that big a waste of fabric. I would rather be safe than gritting my teeth upset because those seams and points don't match up because I was too stingy on getting the measurement just right. A ruler with a 45 degree angle marking will help you square up those HST's.

I also round up and trim down. The HST are consistently the size I need and that makes the next piecing step go much more smoothly.

As far as how to do it, here's how I do it. This assumes that you have sewn a straight line when you put the HST together. I also recommend a LOT of starch.

I use the smallest square ruler I have that is bigger than my unfinished square (for a 4.5" square I have a 6.5" ruler). Put the diagonal line of the ruler on the seam with the point at 12 o'clock, and slide the ruler until there is at least a tiny bit of fabric outside the ruler all across both top edges. Trim both top edges, then turn the square around so the untrimmed sides are on the top. Put the diagonal line on your seam, and line up the 4.5" measurement on the bottom two edges and trim. You now have a perfect 4.5" HST with the seam centered.

I have also used Rhonda's method of cutting HST from strip sets (you can find her tutorial in the tutes section). You sew two strips together and use a square ruler to cut the HST out of the middle. I have used this method once and got great results, and I needed 146 HST.

Hope this helps.

Darren

goodness....of course you can round up...it is THE best way!

Oh duh. I just realized I don't have a square ruler (would you believe???) AND I am an idiot - I forgot all about doing HST using strip sets!!!! Of course I already cut all the danged squares this morning before work. Hmmmm.

So I think i will jury rig a square using either sandpaper or a piece of plexiglass if i have some left over from another project (don't ask :)) - don't know when I will get to Joann's again and I am under a bit of a time crunch with this thing. Now at least I know how to use the square - believe it or not it always puzzled me ( I have a big time directionality problem!) So all the advice helps out a LOT - as usual, you guys are GREAT!