How to Sew a Fitted Sheet from a Flat Sheet
Many households have an excess of flat sheets but often lack fitted ones. This could be due to the fact that fitted sheets wear out quickly, leading to their disposal while the flat sheets are retained. However, there is a simple method to repurpose a flat sheet into a functional and attractive fitted sheet.
Follow this step-by-step tutorial to learn how to transform a flat sheet into a fitted sheet (Note: These instructions are for a queen size mattress, but you can adjust the measurements to suit your own mattress).
Begin by measuring your mattress’s height. A standard queen size mattress measures 60″ x 80″. Keep in mind that mattress heights may vary.
In this example, we are sewing a fitted sheet to cover an unsightly box spring, so the mattress is shorter than the average at 8.5″ tall.
Add the height measurement to the width of your mattress. Repeat this step with the length. In this case, the new width is 77” (60 + (2 x 8.5)); the new length is 97” (80 + (2 x 8.5)).
When buying a sheet, check that it is at least 16″ larger on both width and height. An ideal sheet size would be 95″ wide by 113″ long. If buying a flat sheet to convert into a fitted one, consider getting one size larger than your mattress.
If the flat sheet is not the correct size, this tutorial can help you achieve your fitted sheet desires.
When fitting a sheet onto your mattress, it is ideal to have an extra 8” on all sides for easy tucking. However, even with just an inch or two, the sheet will still fit. To determine the difference, subtract the width and length of your mattress from the actual flat sheet size.
In this case, the difference is 13” in length and 5” in width. Remember to divide these measurements in two, as they are shared among the sides of the mattress. Therefore, we only have 6.5” and 2.5” extra to hold the elastic and tuck under the mattress.
While it may not be much, it will suffice.
To determine the amount to cut from each corner of your flat sheet for alignment, add the extra inches per side to the mattress height. In this case, adding 2.5″ to the 8.5″ height yields 11″, then subtracting 1″ gives a true total of 10″. Thus, on each corner of the sheet, cut 10″ from the length edge and 14″ from the width edge.
While ideally, perfect squares would be cut, I preferred to keep extra cushioning on the sides to ensure a nicely fitting and secured fitted sheet.
Lay out your sheet and cut out all four corners based on your measurements.
When you’re done, your flat sheet will look like this (except double, because you’ll be able to see all four corners cut out in real life).
The next step is straightforward. In one corner, fold the two freshly cut edges (10″ and 14″ cuts) together, with right sides facing in. Your sheet edges won’t match up if you cut out a rectangle, but that’s okay for now.
Sew the cut edges together in a straight line towards the sheet edges, starting at the 45-degree fold.
While you’re here, you may as well zig-zag stitch along the cuts to minimize fraying when your sheets are washed. Repeat for the other three corners.
Lay your flat sheet on a surface, with your new seam lying flat. You can see the difference between the 10″ and 14″ cuts.
To deal with this discrepancy, cut a narrow triangle from the end of the 10” cut along the 14” edge.
Your goal is to smoothly transition from the 10” end to the 14”, losing as little fabric as possible. Trim as much or as little as you like. This won’t be visible on your sheet when it’s on your bed, but the smoother your transition, the easier it will be to sew your elastic hem/casing.
Repeat for the other three corners.
Set your sheet aside while you prepare your elastic. Use 3/8” to 1/2″ wide elastic and go all the way around your fitted sheet for the best fit.
To determine how much elastic you’ll need, fold a queen-sized fitted sheet into fourths and measure four lengths of relaxed elastic against that. I used about 4-1/2 yards of 3/8″ braided elastic, but the amount may vary depending on your mattress size and fabric overhang. Less fabric overhang requires slightly more elastic, and vice versa.
It’s time to sew your elastic hem. Since we don’t have much fabric (we want to maximize every inch, because on one side we only have 2-1/2”), we only want our casing to be as wide as necessary to fit our elastic. Fold the hem over as wide as you think you’ll need, keeping in mind you need to include a little extra fabric for the seam.
When considering hem fold, compare it to the elastic. Also, determine where to place the hem for the elastic to fit around the sheet.
Begin sewing the hem/casing, setting the elastic aside. Sew all the way around. Smoothly transition from 10″ to 14″ (or your specific measurements) with some flexibility in your sewing. Don’t worry about it too much since it will be hidden under your bed and not visible.
Just be careful not to sew a narrower seam than the width of your elastic.
After sewing your hem/casing almost all the way around the mattress, stop approximately 2″ from the starting point. Complete with a back-and-forth stitch to seal it.
This gap is where you’ll start and stop your elastic.
Use a safety pin to attach one end of the elastic to a nearby seam or object.
Use a second, larger safety pin to pin the other end of your elastic. The larger the safety pin, the faster it will be to “thread” your elastic through the hem/casing, although you can only use as big a pin as your hem allows.
To make your sheet hem, thread the safety pin through one side of the gap and push it around.
The best way to do this, if you’ve never done an elastic in casing before, is to scrunch up as much fabric as you can onto your safety pin.
With one hand, pinch the front end of the safety pin to hold it in that position in the casing. With your other hand, pull the bunched up fabric away from the safety pin along the elastic line. Repeat this process as needed, moving the fabric down the elastic to make room for more fabric.
As long as the safety pin keeps moving forward, there is no need to worry.
When you reach the end, thread the large safety pin back through the gap. Don’t worry about there being too much elastic; it will even out soon. Right now, you need the extra length because you’ll be sewing the ends of the elastic together in a flat joint.
Place one end on top of the other, sew together with a stretch stitch, and pull the remaining elastic into the sheet hem.
You’re welcome to sew up the 2″ gap at this point. I chose not to because it won’t be noticeable and it’s not causing any harm. I’m lazy like that.
You’re done! Go ahead and put your “new” fitted sheet on your mattress. Or, in this case, on your box spring.
It fits perfectly. Not excessively tight, just comfortable.
There was enough extra length to pull the fitted sheet down over the bed frame to hide the plastic corner guards. Hallelujah.
I hope you enjoy DIYing your own fitted sheets now and in the future. It’s a great way to repurpose old flat sheets and save money! Happy DIYing.
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I’m Kevin Brown, a dedicated home master and the creative mind behind rentcheck.me. My journey began with a passion for ensuring homes are not just structures but sanctuaries that reflect comfort, safety, and happiness.
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