Need help figuring out size please!
 

I'm piecing blocks that end up at 8 inches. I want to add a 2 inch strip around them and then add QST's around the block but I can't figure out what size to make them. I'm terrible at this. Can someone help?
TIA!!

So, after adding a sash of 2" to an 8" finished block your block will now finish at 12" sq. How large a qst and what orientation?? If you did 2" sqrs of qsts your finished block would measure 14 and maybe look something like this???

Ok, when we frame a block we have to remember that goes on each side, so an 8" center with a 2" frame is now 12" (8+2+2). I had a project like that last year where it started with a 6" block and a 2" frame and I was designing for 8" and was somehow surprised when it came out a lot bigger at 10"!

So it depends on how big you want to make those QST, can easily be 2", 3", or 4" inches for the total of 12". Remember that you also need one for the corners, so add that to the count.

I don’t try to do the math but draw blocks on graft paper and then measure.

This is what I mean- I don't know what size to make the triangles.

Ah! So in this case you want to attach the corner triangles cut at right angles (no bias) so you would start with two squares that you slash along the diagonal. For me the simplest and easiest way is to cut large and trim down to desired size. With that in mind, I'd use the same size squares as what I am framing, that is, with 8" frame, I'd slice an 8" square in half and have quite a lot to trim down (about an inch or more).

Otherwise, there is math involved and there are charts :)
Here's one site:
https://www.generations-quilt-patter...triangles.html

My web quilter has a lot of help, here's the portion for exactly what you want:
https://mywebquilter.com/CalculateSquareinSquare.aspx

If my assumptions and math are correct:

When the triangles are attached to the square, there will be "dog ears" from the triangles - approximately 3/8 inch sticking out on each side. Those get trimmed off later.

Thanks for the chart and all the info. I'm really bad when I don't have a pattern lol :)

Just checking back in to see if you had responded - sorry that I misunderstood what you were trying to do. My only addition to all that great info that bearisgray and Iceblossom gave you is not to skimp on those triangles (imho). Depending on how you are setting the blocks, I tend to to try and cut them so that the outer edges of the corners are on the straight of the goods. That would mean using two 9 3/8 inch squares each cut once on the diagonal. That being said, I always cut them a minimum of 1/2 inch larger that what is called for (in this case about 10"). I match and pin the center points before sewing. This gives me a little extra wiggle room on the outside when I trim up the block.