I've found that making a "test piece" from the strips of fabric before doing major cutting is well worth the time and materials. (Nothing new here, either)
Test piece is made by (and there are variations on this theme as one's preferred length and width of strips)
1) Cut a strip of fabric 1.5 (1-1/2) inches wide by 5 inches long (your measurements) from at least four fabrics (if using less than four fabrics, cut two strips from one of the fabrics that you are using)
2) Sew them together using "your" 1/4 inch seam
3) Press the unit as you would usually press it
4) Measure the unit - the "expected" size of this piece would be 4.5 wide x 5 inches long (4-1/2 x 5)
5) If it is something different than that, here are some places where variations could have taken place:
1) If the fabric was not washed before cutting it, and one used steam while pressing it, it could have shrunk
2) Cutting - I used to think that all rulers were created equal! They aren't. Measure the size of the cut pieces. For example, as far as I can tell, the guideline that I'm using on my ruler is "exactly" 2-1/2 inches from the edge of the ruler. When I measure the cut strip, it's actually a bit more than 2-1/2 inches.
Now, I don't know what the width of the strips would be if one is using a die-cut machine or a June Tailor shape cut ruler - it may be "exactly" the width expected, it may be narrower, it may be wider. Or if one is using precut strips. Measure them.
Some rulers have very wide markings (Quilter's Rule, for example) - and where one chooses to place the line can make a big difference on the final size of a piece.
3) Sewing - seam width - I use 1/4 inch grid graph paper or lined index cards to see where 1/4 inch is on the machine I'm using. I line up the edge of the presser foot with one of the lines, bring the needle down and sew a bit - then I can see where I should place the fabric in relation to the edge of the presser foot. The blocks seem to turn out better when consistent seam widths are used.
4) Pressing - I learned that if I pressed/ironed fabric after I soaked it with starch or sizing, when it was still wet, that many fabrics STRETCHED. I think one is supposed to let it dry, and then press. I usually avoid starch/sizing because of that. Anyway, I try to press with the grain of the pieces - I also try to have the outside pieces of the unit be on the straight of grain. It helps keep the block more stable. Also, make sure there are no pleats by the seams.
I had made a couple dozen blocks of one pattern - and then I made one of another fabric, and the block is about 3/4 of an inch smaller! Somewhere along the line, I changed the recipe!
When possible, it's good to use the same ruler when cutting (or the same variance on the pieces), the same machine with the same presser foot and/or settings, and to press in a consistent way.
What brought this to mind -
Our group was going to make charity quilts - and the guidelines were:
Cut 1-1/2 inch strips
Sew four strips together with 1/4 inch seams
Press the strips
Cut the strips into 4-1/2 x 4-1/2 inch blocks
Very few of the strip units measured 4-1/2 inches. I think we ended up making the units 4-1/4 x 4-1/4
(Which is why I prefer to play "beside" rather than "with" on group projects - but be that as it may - - -)
The whole point of this is to help someone achieve the expected (hoped for!) size of a block - and to maybe help someone find where a variance occurred if the block didn't turn out to be the expected size.