How to Get an Accurate 1/4″ Seam
Updated: Sep 4
“What foot do I use to get a 1/4 in seam (or a scant 1/4″ seam)”? What needle position? HOW HOW HOW???
Our depiction of a seam. The maroon marker is “thread”
To better understand this, we have to accept some facts about a 1/4″ seam. I think we would all agree that a 1/4″ in seam is created by sewing a seam where the thread line is 1/4″ away from the edge of the fabric. But really, do we measure from the center of the seam line (where the needle pokes the fabric)?
Do we measure from the edge of the thread far side of the edge? Do we measure from the edge of the thread closest to the edge of the fabric? If we’re not measuring from the edge to the center of the needle poke, what thickness of thread are we using? If we’re going to get super technical, yes, the thread width matters, whether you measure from one side of the thread or the other matters. This may be the origin of the “scant 1/4”, which may be trying to suggest that we consider the turn of the fabric (the effect that occurs when you fold the fabric over and it shrinks ever so slightly due to the thickness of the fabric and the fact that it’s virtually impossible to crease the fabric in such a way that doesn’t lose a wee bit of width)
You may be asking “But bobbin…seriously! The thread is thin, my needle is thin, how can any of this make a difference?” Hey guys, you wanted a perfect 1/4″ seam! Lots of little hairs here and there add up to a “less than perfect 1/4in seam!”
Back to the story, We measure a 1/4″ seam from the edge of the fabric to the needle poke. Meaning, if you’re using a handy dandy Omnigrid ruler, we insert the ruler under the presserfoot, then HAND PLACE (meaning with the HAND WHEEL), the tip of the needle onto the 1/4″ line – the super thin one! The place to put the edge of the fabric would be the edge of the ruler when the needle is on that line. Personally, we do not mess with scants, hairs etc.
Omnigrid ruler proving that the needle stick to the edge is indeed 1/4″!
If you measure from the middle of the needle poke (meaning, the tip of the needle prior to the needle inserting into the fabric), then we don’t have to worry about the size of the needle. As long as you’re not using super thick thread and a size 18 needle (something you shouldn’t do with quilting cotton!), measuring from the needle poke to the edge should be the most standard/accurate measure.
Which Foot Should We Use?
Great…now we know how to measure our 1/4″. WHICH FOOT DO I USE? Let’s look at the fallacy of the foot. First, we definitely agree that so called “1/4in feet” are great. We’re glad they were invented and we use them all that time. However, the fallacy of the foot is in the assumption that it is the FOOT that causes the needle to poke exactly 1/4″ from the edge of the fabric. Until we invent fancier machines that have sensors that FORCE the fabric to feed a perfect distance from the needle, it is YOU (yeah YOU) the sewing human that controls the edge of the fabric and its relationship to the needle poke.
You may have to trust us on this one, but when we took the photo above with our Omnigrid ruler, the edge of the ruler was aligned with the edge of the foot. This is a 37 foot (just for your reference) on our Artista 630 machine (a max 5.5mm stitch width machine). So, this means, if you ascribe to our “needle poke” theory of the 1/4″, then, aligning your fabric to the edge of this foot will give you the perfect 1/4″. This assumes that your “aim” is perfect. You can use that perfect foot and if the fabric isn’t aligned to the edge, you will not have a 1/4″ seam! Some people have very good eye-hand coordination and can do this consistently. Some people sew faster than they can “aim”, thus creating a less than perfect 1/4″ seam. Most people can aim correctly at slower speeds – a good use of that speed slider! Practice folks…practice! Start slow, work your way up. It’s ok…we all need practice.
Are we saying that #37 is the only foot that can do a 1/4″ seam? Absolutely not! Any foot can do it. A piece of tape could do it. Any reference to aim your fabric edges to is all you need. Some people think that #57 is better, some people like #97. Some people like #20 or even #1 with the needle moved over. Any combination of needle positions and feet that give you results is the “right” answer.
The only questionable method would be a 9mm #20 (C or D) with the needle position shifted to achieve a 1/4″ seam. The reason for this is that #20 is very open in the center, particularly in a 9mm stitch width foot. This means that you have very little support for the fabric in the center. This could cause flagging and other issues. Nevertheless, if you use like this combo and it works for you, GREAT! Go for it. It’s not a combo we ever want to try. Frankly, we don’t like foot #20, but that’s a whole different story.
Is it the Foot or the Needle Position that creates a perfect 1/4″ seam?
So, when people ask “Which foot”, “Which needle position”, it may sound like a simple question. It’s not! It’s a subjective decision, dependent on your own preferences, you seating position, your eyesight, your personal eye/hand coordination ability and your skill level. This question is answered with multiple conflicting answers that can only be resolved by you trying it for yourself.
How Important is it that the seam is exactly 1/4″?
Well, let’s consider that there are three factors to precision piecing:
the fabric weave itself (we explain in more detail on our blog article here)
Let’s assume you have quality fabric, you cut the pieces accurately, then yes, an accurate seam is important.
In these cases, consistent seams are enough, it doesn’t matter what size it is.
Let’s say you have a CONSISTENT seam but it’s not necessarily a 1/4″ – it’s a “scant” 1/4″. Consistency will get you very far when piecing with squares – squares will hide many sins. Piecing rectangles to rectangles may work too.
This pattern will be more troublesome without accurate seams
However, where there are multiple pieces being joined to a solid piece of fabric, you really need accurate seams or adjusting the solid piece to compensate for inaccurate seams. If you have consistent seaming, you can adjust the measurement and it’ll be “easy” to deal with, but may result in an odd sized block.
In the case of angled seams, you will have trouble with matching points unless they are accurate seams.