Squares With HST's
 

If I make this with the squares being three inches, what size would I want to cut the other squares for the triangles?

It's been a few years since I last did something with triangles and I have forgotten the formula.

Assuming you want the HST seam to be on the bias, you take your desired HST size and add 3/4 inch to it. So, in your case you want to cut 3.75 inch squares and use them to make your HSTs. (Details can be found here.)

Can't help, that is beautiful, would make a stunning quilt using those colors.

sorry, platyhiker, but one should add 7/8" to the finished size. however, I add an inch and then square/trim them up to the desired size.

I would simplify everything and cut the "solid" squares 3 1/2", and for the HST's cut them to measure 4 1/2". Sew the HST's, and trim down to 3 1/2, as your solid squares would be. All squares would then sew out to be a finished 3" size.

I believe I'd heard that some time back. I'd rather have to slice off a smidge than have them be too small.

Boston, you could make the 8 at a time HSTs! No bias or anything! (For 8 at a time I use finished HST size + 2" - not 1 7/8')

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There are other copies of the method on line.

Or you can cut 3" strips and then cut your triangles from the strips using the Easy Angle ruler. It's the method I use and is very accurate. I rarely trim anything off.

Happy Birthday, Boston! <:)

Thanks sewbizgirl!
And thanks for the neat suggestions.