Why a 1/4" Seam Allowance Matters

I'm not a diehard quilting rule follower. In general, I think the quilt police should mind their own business! But there are some rules I do stick by, and the 1/4" seam allowance is one I never break when precision piecing.


A long time ago, I met a very ambitious newbie quilter. She was the nicest lady and was very enthusiastic about learning to quilt! She chose a log cabin block as her first. In my opinion, this is a very good choice for beginners because it's a beautiful and fairly easy block - all straight seams and no half-square triangles.

Each month, she'd bring her completed blocks to guild for show and tell. After a few months, someone asked her about what seam allowance she was using because the blocks were all - well, they were just "off." She suggested she should try a 1/4" seam allowance.

"Oh, I don't worry about seam allowance," she said, laughing. "It will all be okay."

Over the next months, she completed the blocks - all 49. She brought them to an open sew day to set them together. She carefully and thoughtfully laid them out. Some of the blocks were as small as 11" and some were as big as 13 1/2" (They were supposed to be 12 1/2"). At this point, she didn't seem to notice.

She started sewing them together. After a few rows - in addition to the mismatched sizes - the blocks were either bowing or cupping where the seam allowances weren't straight. The outer "logs" of the log cabins were all misshapen, some completely missing.

After a few rows, she began to understand that something was wrong.

She asked for advice and after a lot of group discussion, she learned a few truths about seam allowances:

1. An accurate, straight seam allowance helps your block lay flat. If you sew a seam that curves toward the left, your block will bow. If the seam curves to the right, it will cup. Both situations are problematic when pressing, and later when quilting. Neither the block nor the finished quilt will lay flat and there very well may be puckers.

2. Using a 1/4" inch seam allowance will not only make all your blocks the size they are supposed to be, but when joining them together, they will fit. This is especially important if you have points at the edge of the block - the point tip will not be cut off when it's joined to the next block if all the blocks are sewn accurately.

3. If all your blocks are the right size, it will make the borders - especially pieced borders - fit without redrafting the pattern. Borders that are too big will cause rippled, waving edges. Borders that are too small will create a top center with too much fullness, causing puckers where the top center and the borders meet. If all the blocks are the right size, the pieced border will fit making the quilted quilt flat.

4. When participating in swaps and group quilts, yours won't be the one thrown out because it doesn't fit. This will also keep swap partners and opportunity quilt chairs happy if your block is identical to the rest!

The newbie quilter learned a lot about quilt block construction that day and now, all these years later, she is a seasoned quilter with many fabulous quilts under her belt. She often laughs about her early tribulations, and will willingly discuss the importance of an accurate, 1/4" seam allowance with any new generation quilter who wishes to learn from her mistakes!

To get an accurate seam allowance, I use a 1/4" foot made for my sewing machine. I highly recommend investing in one if you can. If you don't have one there are several methods to check for accuracy and to mark your machine so you'll always get that perfect 1/4" seam allowance. Search: "perfect 1/4" seam allowance" for resources.

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