quarter square triangles

I never remember that stuff either, so I get out a pencil, ruler, and sheet of paper and draw it, beginning with one triangle, adding the seam allowance all the way around the triangle butting another triangle and seam allowance next to it, and then measuring the total. Easier than formulas!

Like Mary I consider it safest to draw and measure, but I seem to recall that you take your desired size and add 7/8s. I know somebody will sing out if I am mixing up my remembers.

NightMist

I also draw them to be sure! but the number to add is 1 1/4" to the desired *finished* square size. . In message , NightMist writes

The Chart for all of that is on page70 of QNM September 2005. Find it, copy it and keep it available in your sewing area. It is a winner. It also shows some neat stuff to do with what is basically a flying goose. Polly

"Patti" I also draw them to be sure! but the number to add is 1 1/4" to the

LOL, my kinda math.

The "formula" is that you add 3/8" to the "regular" measurement for every 45° diagonal seam. So, for HSTs you add 7/8" to the *finished* measurement and 1 1/4" (double 7/8) for QSTs. Not really much different from remembering to add 1/2" for seam allowances to squares/rectangles.

Pati, > I know I have heard this discussed before but can't for the life of me

WOW Jennell, I wonder why I never knew about this place before. It certainly has answers to more questions then I would ever ask. Thanks.

Thanks Patti, what is QNM?

Quilter's Newsletter Magazine.

--Lia

The traditional formula is add 7/8". I just add 1" and trim them down. Makes my life SO much easier. :)

The formula for HALF square triangles is to add 7/8" inch. Many quiltmakers prefer to add one inch and trim it down.

The formula for QUARTER square triangles is to add 1 1/4" inches. Similarly, many quiltmakers add 1.5" and trim it down.

--Lia

Pati, I must be missing something here. How did you get from 3/8" to

7/8"? And doubling 7/8" gives 1 3/4" .... I'm confused! I do know that 7/8" is the "magic number for HSTs and 1 1/4" is the one for QSTs, but I'd love to know *why*.

Ha! That is why I draw and measure! Just relying on memory, one of these days I would do a block using Avagadro's Number for one of the measurements.

NightMist

Okay, it is fairly straight forward. The math involves square roots of odd numbers and such and I am not up to doing it at the moment . But if you have a finished size of square that you need, you add

1/2" for seam allowances. If that seam is a 45° diagonal seam you need to add an "extra" 3/8" for the ears that are, sometimes, trimmed off. Check any of the templates or "triangle trimmer" tools to see what I mean. Or just draw your triangle, add seams, then draw a line perpendicular to the grain 1/4" from the 45° angle. If you do this with a square, draw a diagonal line, corner to corner, then at the ends of that line draw a 3/8" square, you will see that you end up with quarter inch seam allowances all around.

I h> >

You are exactly right. Duh. (Note to self -- do not answer any questions before adequate caffeine is in system.)

What you are adding to each seam allowance is 1/4" times sqrt(2) (remember the Pythagorean theorem about right triangles?), which gives about 3/8" for each seam.

Why 7/8" instead of 3/4"? While 3/4 would work, you'd need to trim away

43/1000". With 7/8" you can trim away just over 1/8", which is more manageable. I find 7/8 to be a PITA to measure, so I add 1" and trim away a bit more. 1-1/4" shouldn't work for QST. You need to account for 4 seam allowances, and if you do the math that is 1.414", which is more than 1.25". Methinks Pati meant to write 1-1/2" or 1-3/4" for the QST -- either would work.

I just put a fresh pot of coffe on, anyone in need is invited.

Aha! Thanks, Kathy! :)

I've always been told to use 1 1/4", so there must be some reason. Not that I know what that is .... ;)