When is an Inch not 1″?

Have you ever compared the markings on your rulers to the markings on your cutting mat to see if they are the same? Can you even imagine that they wouldn’t be? Are the markings on your rulers really accurate? Is that inch really 1″?

It never occurred to me that the markings on the rulers might not match up with the markings on the cutting mats, nor that the rulers that I’ve used all these years weren’t really accurate themselves. I mean, why on earth would I even think about that? These things are precision made and we trust them to be accurate, right? Well, I used to anyway.

I found out recently that my trust has been misplaced for many years. I’m having a ruler manufactured to go with my book (yay!), and the manufacturer sent me a prototype to approve. I needed to make some changes, and in doing so, I measured the ruler against one of my Omnigrid rulers, and guess what? One of them was off ever so slightly. I assumed it was the prototype; after all, it’s just that, a prototype, a sample. Maybe it just didn’t get cut right (which was going to be another whole can of worms anyway, but I digress). So I emailed the manufacturer and told him I thought that the prototype he sent me was not the right size.

Unfortunately, assuming did what it frequently does, and made an a** out of me. The manufacturer told me it was exactly the right size, and asked why I thought it wasn’t. I finally got out one of my grandfather’s old stainless steel drafting rulers (he was an engineer, and I figured that one of those rulers would probably be a good benchmark), and compared it to both the prototype and the Omnigrid rulers. The prototype proved to be exactly the size it needed to be to cut accurate fabric pieces, and the Omnigrid ruler was off! Not by much, but the inaccuracy was there as plain as day.

At that point, I went a little nuts, and started comparing the drafting ruler to all my rulers, which are all the Omnigrid brand. The worst of the bunch was the 6″ x 24″, and though the drafting ruler is only 18″, I could tell that the Omnigrid ruler was nearly a sixteenth of an inch longer down at the 18″ end, if the 0 ends were lined up. I truly believe that at some point, this can make a difference in whether your patchwork pieces will fit together as they are supposed to, or need easing and heavy steaming to make it all work out as planned.

When you’re piecing a simple block there probably won’t be any evidence of a problem, but when you’ve pieced 40 complex blocks with many pieces and are stetting them together the inaccuracies add up, and then things don’t go together properly. And maybe, with all of the other stuff going on like 1/4″ seams being accurate (or not), and fabric stretching (or not) and grainlines going every which way, this whole issue with the rulers is just one more bump in the road, but heck, who needs another bump?

In the midst of these maybe-not-so-scientific experiments, I laid the 6″ x 24″ ruler on my 24″ x 36″ Olfa cutting mat, and got another eye-opener. The mat wasn’t even the same as the Omnigrid ruler. For that matter, the mat wasn’t precisely accurate either when measured against the drafting ruler, but it was off in the other direction. 😯 The markings on the mat were actually smaller than they should have been at the 18″ mark.

Now, maybe it’s not quite clear why this was bugging me out so, but I’m getting to that. In general, I don’t use the lines on the mat for anything, and I almost never measure against them, unless I’m working on borders. Borders are soooo long, and cutting them to the right size for the quilt can take some creative measuring and ruler manipulation (I don’t sew them on and then trim!), and I do use the mat at that point to measure the quilt top if I can fit it on there by folding it in half or something. I’ve always figured it was a better bet to measure the quilt top against the mat, rather than with a measuring tape, since those can stretch over time.

So when I measure the quilt top on the mat which is shorter than it should be, but then cut the borders with the ruler which is really longer than it should be, what happens? The borders are too long. Sometimes as much as 1/4″ to 1/2″ too long, and even that small amount can cause waviness in the borders, especially when combined with other issues in the quilt interior that may be giving the whole thing a flyaway look before the borders are even attached. And yes, I’ve noticed this during construction, that the borders are too long when I’ve just cut them according to the measurements. I’ve even gone back and double and triple checked everything to make sure I wasn’t just having a blond moment, but if you use the same tools and method to check your work as you did to do the work, you still don’t get the right answer, obviously.

All these years, I’ve been soooo careful to cut and sew accurately so that my quilts are flat and straight, but I’m still ending up with wavy borders at times, and wondering why. So now I know that I’ve been defeated by the ruler/mat combo. I’d already purchased a new Olfa mat for my cutting table when I discovered all of this, I just hadn’t put it on yet. I decided to measure the new mat and see where it fit in, and it doesn’t measure the same as the Omnigrid rulers either, but it is better (meaning more accurate overall, and closer to the Omnigrid ruler measurements) than the old one.

So what does all of this mean? Well, Crazy Accuracy Freak Girl is blubbering in the corner and will probably be there a while, but as for me, I just need to remember to use either the mat or the ruler to measure for borders or whatever it is at the time, but not both. So check your rulers people, and think about how you’re doing things that might be causing a problem without you knowing. An inch isn’t always 1″.

8 thoughts on “When is an Inch not 1″?

  1. I was taught not to use the markings on the cutting mat because they never match up (as you figured out). I never figured that the rulers would be different! Actually, I’ve neglected to do what my head has been telling me to do for ages – compare all your rulers to each other. My bubble has been burst!


  2. Hi Erinn, and Welcome! Wow, I must have missed a major fundamental concept by not ever taking a beginning quilting class. I always just told my students that they should ignore the lines on the mat when rotary cutting, but not because they were inaccurate. It was more because you really don’t need to confuse the issue by lining up the fabric on the mat, and then lining up the ruler on the fabric, and all you really need is the ruler and the properly folded fabric to make a good cut.

    I never heard or read anything that led me to question the accuracy of the lines on the mat, or think that they might not be the same as the lines on the rulers. I guess I’ve been livin’ in the dark all these years!


  3. I was taught the same as Erin that the mat rulings weren’t accurate so don’t use them. I hadn’t ever checked the markings on my rulers but have occasionally thought that perhaps I ought to. Now I will have to coz my very own Crazy Accuracy Freak Girl isn’t going to happy til I do! Thanks:-)
    I have also tried to teach others not to mix mats and ruler markings but most think I am nuts and just ignore me, well ha its seems I was right!


  4. Yikes! I’ve never taken a quilting class and so, have blissfully assumed (ha, silly me!) the rulers, mats, tape measures, etc., are all in synch. I LOVE the fact you’ve proven I am not completely inept … all of those 1/16″ DO add up. I’ve shed a tear or two at the end of a few projects over the years, wondering why measurements are off.

    You ARE my hero! Thanks.


  5. Yes, I know that no ruler is created equal. It drives my OCD nuts. Why is 1/4 inch different on each machine?? If I line up my rulers where the needle is and move over 1/4, it doesn’t match with my guide! So now what?? If nothing is accurate between anything, why do I even bother?? What about the inside or outside of the mark?? What about your pencil marks? Do you use a regular pencil or mechanical one? You gotta love OCD. You can laugh..I do it all the time.

    None of my rulers match. Even the same brand rulers don’t match. My rotary cutting mat doesn’t match with anything either!

    My solution: I don’t care anymore. I go by my so called 1/4 inch on my machine. If that means my quilt block is 9.2 inches instead of 9.5, so be it. I don’t like fiddling with my needle position on a machine either just to make it fit with my rulers. I like the Creative Grids because I can see what I’m doing and the lines are nice and fine.

    Once I gave up, I’ve enjoyed quilting so much more. My OCD can only take so much. LOL!


  6. Wow this astounded me! I am pretty new at quilting, well accurate quilting, but still, I can see why I didn’t have much success at first. The last one I did, I followed Sharon Schamber’s advice of spray starch and ironing and the last quilt I made turned out perfect!
    See this post to see the quilt I made And when I say perfect, I mean :As long as when I fold it, all the corners come together and nothing sticks out.
    Thanks for the wonderful insight. I now feel a bit OCD myself. I always trusted those rulers. How RUDE!
    Have you found anything, besides the drafting ruler that really is accurate?
    thanks for your beautiful website and all your posts. You are Amazing.


    1. Hi Annie and welcome! Your quilt is truly wonderful and it is perfect!

      I think the thing to do is just be aware that not all measuring devices are equivalent, and work accordingly. It’s not like I use the drafting ruler for quilting, I just used it as a comparison tool because I figured that it would be the most accurate thing in the house. It’s more important that the tools you use on your quilt are accurate in relation to each other, which is where the problems have surfaced for me. As I said, the new mat is closer to the ruler measurements, and now that I’m aware of the problem, I can compensate when I’m measuring and cutting borders for my quilts.

      Thanks for visiting, and sharing your beautiful quilt. Good luck with all the rest you’ll be making! 🙂


  7. I have just realised that my rotary cutting mat is completely inaccurate. What really annoys me is in Australia you can easily pay up to $90.00 for a 23″ x 35″ board. It is made by a well-known company. I have used every kind of ruler & tape I have in my house & all the marking on all the rulers match up, but not the cutting mat. For us to simply accept this fact is beyond me. What does it take to make sure the markings are accurate. I contacted the company that makes these mats & after 24 hours they got back to me saying all the mats in their warehouse are okay & they have never had a complaint. Yes they have, Me. I am really annoyed & so fed up with companies that produce, quite frankly, faulty merchandise. I have to take the mat back to the shop I bought it from today & I am probably going to have a fight on my hands. This is not good enough for consumers. If your mat isn’t accurate take it back & complain to the company. Make them take responsibilty for the quality of their products. If you can buy a 50 cent tape measure & it is accurate why accept that an expensive item like a cutting board is inaccurate. Not good enough.


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