How to sew an accurate 1/4 inch seam
One part of piecing a quilt top where all the pieces fit together nicely is sewing an accurate ¼ inch seam.
In the video below I discuss how exactly to make sure your seam is the accurate 1/4 inch you need to make your piecing turn out beautifully.
And if you’d prefer to read…
A 1/4 inch seam guide is not enough
There are a couple basic methods out there for ensuring you are sewing a ¼ inch seam when making your quilt tops:
- Using a guide on your machine- even just masking tape. or
- Using a special foot
And these techniques do work at making sure your seam is consistent – that all your seams are the same width seam allowance. And consistency is definitely important.
If you’re having trouble sewing consistently or in a straight line, check out my post How to sew in a straight line
Consistent seam allowance vs. accurate seam allowance
But if that consistent seam is not actually the right width, your pieces, especially triangles, will not line up and your blocks whether they are triangles or squares will not end up the right size.
Which means your quilt looks wonky, or just turns out the wrong size.
It doesn’t take much. A seam allowance that is just 1/32” off means that at each seam the sewn block is 1/16 inch off (1/32 on each side). When sewn on a quilt that has just 16 seams across the quilt – that’s a whole inch off. On a block with 4 seams, it’s ¼ inch off.
If you take that block with four seams that aren’t accurate – in the picture below the seam allowance is 1/32 inch too big – and try to sew it to a block that just has one seam – the sides aren’t going to match.
That’s because you cut the bottom squares of fabric thinking that the completed block on the top would be a certain size – using an accurate ¼ inch seam.
If you try to match them up you’re going to be pulling and tugging and adding some ease or puffiness. Your quilt top won’t lay flat.
It’s ALWAYS up to you as to whether that bothers you!
If you want everything to match up, you need your seams to be accurate. You have to do more than just using something that make sure they are consistent. You have to make whatever seam allowance you are sewing consistently accurate.
How to check a 1/4 inch seam allowance
Your first thought might be, I’ll just measure the seam and see if it’s right.
But what really matters is what the RESULT of that seam is.
With every seam there is some extra space taken up by the thread of the seam and the pressing of the allowances to the side. This means it needs to be a tiny bit smaller than a ¼ inch or what is often referred to in patterns as a scant ¼ seam.
So to get an accurate ¼ inch seam result, you’ll need to sew some seams and test them.
I like to do this using two 2 ½ inch strips. I use strips instead of squares because it also gives me some feedback at how consistently I’m sewing.
Cut accurately
When you cut those strips you’re factoring in the second part of perfect piecing and that is cutting accurately. It’s one of those garbage in garbage out scenarios – if you’re starting with pieces that aren’t the right size, it doesn’t matter how accurate your seams are!
Make sure your test pieces are cut exactly to size 🙂
Sew those two strips together with what you think is a ¼ inch seam. Press them. Measure the width of the result. It should be exactly 4 ½ inches wide.
If it’s less, then your seam allowance is too wide. If it’s more, then your seam allowance is too narrow.
Go back to your machine and see if you can adjust your setup to fix it. Move the tape, adjust the needle position, find a slightly different place on your foot to line up to so that the space between the edge of the fabric and the needle is smaller or bigger.
You’re smart, you can figure that out.
Use a new set of strips to retest.
Repeat until you know how to make that seam result in exactly the right width combined piece.
Do this before you start every quilt
Why every quilt?
How you press and what thread and fabric you are using matters. If you press your seams open you might get a different result, if you use thinner or thicker thread to piece, or if you’re using thicker or thinner fabric. Plus it’s a good reminder that you’re trying to do this accurately.
You won’t always succeed. And that is TOTALLY expected! The goal is to enjoy yourself and see this as just a fun challenge to play against yourself – not anyone else.
Because best way to get better is to keep trying, letting the not perfects be part of the puzzle, so that you don’t get discouraged. That way you can continue to get lots of intentional practice and your piecing will get more and more accurate over time.
Because remember, it’s all about HAPPY sewing.
