Custom Sized Fitted Sheets – Tutorial


For some reason, fitted cot sheets do not fit the mattress in Roman’s cot. Not the standard ones, not the ones for cot beds, nothing. Luckily for me, they’re easy to make.

I had an old queen size flat sheet kicking about, and managed to get 2 cot sheets out of it. Given that I also had the elastic, this was a free project. This is a formula, so that you can use this for any sized mattress you want to make a sheet for. I’ve also used this method to make a cover for the change mat.

Fitted Sheet

You’ll need:
Fabric – ideally pure cotton as it’s nice and breathable
6mm wide Elastic
Thread for the sewing machine

How much fabric do you need?
The sheet is a large cross shape, the middle is the size of the mattress, and the wings wrap around the depth of the mattress and make the overhang that is gathered underneath the mattress.

sheet cross

Lenth of Wings = Depth of mattress + amount of overhang you want + about 4cm for seams
I’m using 4cm for the seams as I like to do French seams on the corners and a double fold over to encase the elastic in around the edge*.

Length of fabric = Length of mattress + 2x (Length of Wings)
Width of fabric = Width of mattress + 2x (Length of Wings)

How much elastic do you need?
Length of elastic = 2x (Length of mattress) + 2x (Width of mattress) – 8x (amount of overhang you want)

So for my mattress:
Length of wings = 10cm + 20cm + 4 cm = 34cm
Length of fabric = 140cm + 2x(34cm) = 208cm (2.1m)
Width of fabric = 70cm + 2x(34cm) = 138cm (1.4m)
Length of elastic = 2x(140cm) + 2x(70cm) – 8x(20cm) = 260cm (2.6m)

Gotta love a bit of maths!

When buying fabric, I always buy a bit extra and prewash it in case of any shrinkage. So I would probably get 2.5m of 1.5m wide cotton for this.

Fold the fabric in half lengthwise, then widthwise, so it’s a quarter of it’s size.

Now, you need to cut the corners out to make the cross shape. You would think that they are the size of the wings, but they’re not. You need to take off half of our seam allowance for the corner seams. The 4 outer corners should make up one corner of your folded piece. This is the corner you cut out. You will cut out a square from this corner.

sheet corner

Length of square = Length of wings – 2cm
2cm give you enough to do 5mm French seams and a bit of ease for the sheet

In my case, I get 32cm.
Measure in this distance and mark along both edges from the corner of your fabric (the corner with all the raw edges) Using a ruler, mark a line along one of these points, running parallel to the edge of the fabric. Do the same for the other point. They should meet up to make a square. Cut out this sqare. If you unfold your fabric, you should now have the cross with 4 equal width wings and the middle the size of the mattress.

Now you can finally do some sewing! For French seams  match up the cut edges of one of the squares, WRONG sides together. Sew with a straight stitch 5mm from edge. Trim off half the seam allowance. Fold the seam the other way around, so fabric is RIGHT sides together. Sew with a straight stitch 5mm from edge. This encases your first seam neatly and makes a nice strong seam for your corners. Repeat with the other 3 corners. If you’d like a visual, I have a tutorial for French Seams here.

You should now have a fabric box. Now to hem the edges. Fold the raw edge under 1cm and then again another 1cm to hide the raw edge. Press and sew it down close to the edge, leaving about 2cm unfinished. Put a safety pin into the end of your elastic and use this to feed the elastic through the hem going in and coming out of the 2cm hole you left. Knot the ends of the elastic together and you’re done!

I like to leave the 2cm of the hem unstitched, so that if I ever need to pull the elastic out to replace it, I don’t need to get my seam ripper out.


*You could make this fitted sheet a bit quicker by not doing the French seams and by sewing the elastic straight onto the edge of the sheet, but I think that by finishing them off a little nicer they look better and last a lot longer.

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  1. Mia says

    Thanks for the great maths – helped heaps! I did however find I used a lot less elastic than your calculation said but I made toddler sheets and my mattress is 160 x 70cm so that could have made the difference. I only used about the same as you did.

    • abby says

      If you want the same amount of overhang that I have and your mattress is about 10cm deep, then you’ll need 1.4×2.0m

  2. says

    I would like to put elastic in a casing around the top and a bit off to the sides and then do the same to the bottom and the a bit off to the two sides, NOT sew the elastic all around the who sheet. How much elastic should I use? Thank you.

    • abby says

      I’m sorry, I’m not really sure what you mean. You could simply measure the edges you want to put elastic along and then order that much. You’d have more than you need as it would be the unstretched measurement.

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