Needing some basic information
I had an awakening when sewing along with Edyta Sitar's mystery last year. I just loved the basic way she made her units: For HSTs, cut squares, cut in half diagonally, sew together. For QSTs, cut squares, cut diagonally twice, sew together. My problem is, I can't find the basic information I need, which is, how to figure out what size square to start with when making these units. All the information I find when googling involves less straightforward methods, like making multiple units at a time, oversized units for trimming down, etc.
Can anyone tell me how to determine the size of square to start with based on finished unit size, for HSTs when cutting in half diagonally, and for QSTs when cutting twice diagonally? Is there a formula? Thanks! 
Here's a link to a great chart:
https://jacquelynnesteves.com/halfs...andtutorial/ and for qst https://www.bonjourquilts.com/quartersquaretriangles/ 
Thanks, Julienm1! That first chart will be great; unfortunately, the second link is for a different QST method she prefers, so she doesn't give sizes for that basic, cut the square in 4 pieces method.

Thank you Joe'sMom for asking the question and Julienm1 for the links. I've always had a problem with qst dimensions.
My friend and I made a raffle quilt for our local Commission on Aging that required an insane amount of qst. Since we were making our own pattern we did all the math and I proceeded to cut hundreds (maybe millions or so it seemed) squares all the wrong size. One wouldn't think such a small error would cause so much pain but it did. I now have a guide that I sure wish I'd had at the time. Good news is the quilt turned out greatone we were very proud to own up to! Grammahunt 
For quarter square triangles, start with a square to which you add 1 1/4” to the finished size. If the finished size is 3”, start with a 4 1/4” square. For a 4” finished size, start with a 5 1/4” square. Etc. Many people start with a slightly larger square and trim to unfinished size after sewing.

Originally Posted by Grammahunt
(Post 8449361)
I now have a guide that I sure wish I'd had at the time.
Originally Posted by SuzSLO
(Post 8449379)
For quarter square triangles, start with a square to which you add 1 1/4” to the finished size. If the finished size is 3”, start with a 4 1/4” square. For a 4” finished size, start with a 5 1/4” square. Etc. Many people start with a slightly larger square and trim to unfinished size after sewing.
I guess I could experiment, following what is the apparent 'formula' Bonnie used  double the size of the finished unit and add 1/4". 
1 Attachment(s)
Here’s a chart so you don’t have to do the math.
Joe’s Mom: I rechecked the Week 2 instructions for the quarter square triangles and for what Bonnie called the “traditional rotary cutter math” my instructions show starting with a square which is 1 1/4” larger than the finished size. Maybe she made a correction or you are looking at a different method in her instructions. 
In the Grassy Creek Mystery, clue 2, for making 2" finished QSTs, Bonnie Hunter writes: "If you were working with traditional rotary cutting math, you'd start with 3 1/4'' squares." (The clue then uses strips, not squares, to make elements of the QST, rather than quartering a triangle.)
If you try the experiment, or use math, you will see that cutting a square along both diagonals and sewing it back together yields a square that is 3/4" smaller than the original square (so the finished size is 1.25" smaller than the original square). 
SuzSLO, thank you for following up! I could have sworn I cut 4 1/4" squares for clue 2, but my directions, which I printed out on the clue day, also say what you indicated! Thank you for straightening me out! I was in such a tizzy about it, LOL.
edit Thank you, as well, Playhiker. (We may all have our posts deleted since we are mentioning actual sizes and quoting the mystery text, but I do thank you both for your help!) 
If you are doing 4 at a time with same colors (or 8 at a time) there are 2 helpful instructions for those!
https://www.pinterest.com/pin/222928250277417183/ = 4 at a time https://blocloc.com/wpcontent/uploa...rtforHST.pdf = 8 at a time 
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