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Importance of Seam Allowance in Quilting

Seam allowance is the amount of fabric that is on the inside of what you are sewing. In quilting the standard seam allowance is 1/4”. But how important is it that your seam allowance is exactly 1/4”?

The answer to that is the one that drives my kids crazy. It depends. There is no one-size-fits-all set-in-stone answer.

Getting an accurate 1/4” seam allowance is achievable, but it will take practice and attention. Check out this tutorial for tips to make it easier.



Here are five things that determine how much seam allowance matters:

1. Type of project

Different projects require different levels of accuracy and attention to detail. Before you begin, consider how much accuracy is required and if there are steps in your project where you can correct if needed.

Improv piecing

Improv quilting involves random shapes and pieces and joining together with little planning. Sometimes it is string piecing on foundation papers and sometimes it involves working out from a centre shape.

Patterns like the Wacky star involve stitching random triangles and then trimming down to size.

wacky star quilt

Whichever type of improv piecing you are doing, an exact seam allowance is not necessary. The random shapes and sizes already have a lot of variation, so being off by 1/8” doesn’t matter.

Simple traditional projects

Many simple projects allow you chances to correct as you go. If you are making a Rail Fence quilt and your seams are a bit off, you can just trim your blocks to be squares, even if it doesn’t exactly meet the measurements of the pattern. Your finished size might be a bit off, but an inch or two on a bed quilt won’t matter.

green and floral simple rail fence quilt block.

The same applies to things like nine-patch and log cabin. If you are making a quilt with blocks and some are not quite right, just trim them all down to match the smallest size. It won’t matter if your blocks are 12-1/8” instead of 12-1/2”.

Intricate traditional projects

The more pieces that are in your project, the more seam allowance matters. Consider a 12” block. If it is a 4-patch, there is only one seam horizontally and one seam vertically. If the seam is off by 1/8”, that means the size of the block will be off by 1/8”.

If you have a 12” block like the memory quilt block, it has five seams horizontally and five seams vertically. If each seam is off by 1/8”, then the final block will be off by 5/8”.

green and pink memory quilt block.

Modern projects

Lots of modern quilt patterns have large empty spaces instead of traditional rows of blocks. This can be forgiving with seam allowances, but it also means that if your seam allowances are off, all the cutting dimensions change.

If you cut as you sew and can do the calculations, seam allowances are only moderately important but if you cut everything out in advance, seam allowances are pretty important.

2. Technique

The techniques you use have different levels of flexibility. Think about it before starting a project with a new technique.

Traditional piecing

Cutting shapes with a rotary cutter and stitching them together requires an exact seam allowance. The seam allowance is built into the cutting directions, and variations will throw off all the math.

Paper piecing

Paper piecing, either English paper piecing or foundation piecing, is pretty forgiving with seam allowances. The pieces are marked by stitching lines, so you have flexibility.

Reversible patchwork

Reversible patchwork with modern pojagi seams doesn’t require exact seam allowances. In fact, with this technique you don’t want you seams to line up, so this is a great technique if you struggle with accurate seam allowances.

fabric window hanging in greens that looks like stained glass.

Trimming techniques

Some piecing techniques involve cutting the pieces a bit larger and then trimming down the pieces after they are stitched. This is especially popular with triangle piecing. This makes seam allowances moderately important. You want to be pretty close, but you can fix it if you aren’t exact.

3. Scale of project

The scale of the project you are working on has a lot of impact on the required accuracy.

Number of pieces

The number of pieces matters. The amount your seam allowances is off will be multiplied across the number of pieces you have. A bed-sized quilt with 1” squares requires a lot of accuracy.

Size of pieces

The smaller the pieces are, the more accuracy is requires. If you want to make 3” star blocks, you will need exact seam allowances.

The math will prove this. If your block is supposed to be 4”, but you are off by 1/4”, that is a 6% difference. If your block is supposed to be 12”, but you are off by 1/4”, that is only a 2% difference.

4. Purpose of the project

I think it goes without saying that if you want to make a quilt for competition, everything has to be exact. Corners must line up and points must not be cut off.

However, beyond that, there is a big range of purposes. Quilts can be gifts or personal, they can be for kids or adults. Most quilt uses don’t require 100% accuracy. 

Allow yourself to use some projects as learning experiences. You will get better with practice, so don’t sweat mistakes that you make. If you have a total disaster, you can always use it as a picnic quilt or give it to your neighbour’s dog.

5. Your own comfort level

Everyone has a different level of “quilting OCD”. I admit that I really do want all my seams to line up and it bothers me if corners are cut off. However, I also hate ripping out seams, so I give myself a distance test. If it looks fine from three feet away, I will probably leave it.

Only you know how much something will bother you in a finished quilt. In the end, you will have to determine how important seam allowances are to yourself.


Work to your strengths

Quilting should be enjoyable. Most of us do not live in a situation where if we don’t quilt, we will freeze in the winter. We make quilts to relax and express our creativity.

If you enjoy the challenge of tiny pieces and accurate points, then go for it! People will be amazed by what you make.

If you just want to pump out charity quilts as quickly as possible, then pick simple patterns with a little wiggle room.

If you are a beginner, take the time to practice and learn new skills.

What you enjoy will even change depending on your mood or season. You can switch between projects depending on the day.

There are times when accurate seam allowances are crucial and times when it doesn’t matter at all.

Know yourself and choose your projects accordingly. 

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clear ruler measuring quilt pieces with title "getting an accurate 1/4"

two pieced strips of fabric with title "pojagi seam allowances vs. quilting seam allowances"
Elizabeth DeCroos

Elizabeth DeCroos

designer, teacher, speaker

Elizabeth enjoys doing all types of sewing and needlework and teaching others new techniques. For more information or to have her speak to your group click HERE.

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