Boys Swim Trunks (or underwear!) Pattern and Tutorial


I have finally got around to making Harry some new swimming trunks the night before his school holiday swimming lessons!

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There they both are ready for their lessons in their handmade togs (swimwear for non-kiwi’s!).

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Harry’s swim trunks are not lined as the fabric is very thick and has no risk of clinging or being see-through.  The fabric came from Spotlight and was is called ‘Scuba’, in case you were wondering!

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I was pretty pleased how these turned out so I thought I had better share them with you all.  But Harry doesn’t need anymore swim trunks right now…so I made them out of cotton lycra you can’t have too many pairs of underwear!  Just for the kiwis, reminded me of that Tip Top ad, undies, undies, togs ☺



What you’ll need

  • Stretchy Fabric
  • 25mm (1”) Elastic – 53cm (21”) for size 6
  • Overlocker (can use zigzag on standard machine)
  • Pattern – Free PDF in size 6.


Step 1 – Print Your Pattern

Luckily for you there is now piecing together pages this time, all the pieces are small enough to fit on single pages!  Just print and cut them out.


Step 2 – Cut Fabric

Decide whether you want (or need!) to line your swim trunks/underwear.  If not lining cut one of each pattern piece, and two strips for the leg holes.  If you are lining cut and extra front piece and crotch piece.

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You can see I have two front and two crotch pieces for lining out of the same fabric.

You will need to cut the two strips pictured too.  The dimensions are 4cm (1 5/8”) by 33cm (13”).  If your child has slim or not so slim legs than you can adjust this piece to suit.  Harry is probably about an average size 6, and this size fits just right.


Step 3 – Attach Crotch to Front Piece(s)

I will use black thread on these so your can see what I have done.  You can use matching or contrast thread even a pop of colour…just do what you like!

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Pin the crotch pieces to the front pieces (just one if not lining).  With the right sides facing each other.

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I used the overlocker for this but you can use a zigzag stitch on a standard machine too.

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Here are both front/crotch pieces wrong sides facing.


Step 4 – Attach Back Piece

Now at this point I had a bit of a blonde moment, I am prone to those from time to time!  I was still thinking of the unlined pair and attached the back piece the same way.  So there is a seam inside this pair that doesn’t need to be there.

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I pinned like above and overlocked together.  But a better way would be to pin the back piece in between the two crotch pieces.  See chart below!

Harry Swim Trunks Chart a

Make sure the Front pieces are right sides facing each other (or against the back piece) in the stack.

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As you can see my seam is on the inside of the trunks if you follow the steps in the chart then yours should be neatly hidden inside like the front seam.

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I decided to topstitch mine ( I did for the unlined version too), just to keep it sitting flat and prevent it from being scratchy.


Step 5 – Side Seams

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Time to sew the side seams.  Line up the sides with the trunks right sides facing each other ( inside out!).  Pin in place and overlock together.

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Repeat for the other side.  I decided to topstitch these seams, this is totally optional but it keeps them sitting nicely.

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You can see how the inside seam lays nice and flat.


Step 6 – Leg Openings

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Fold the strips in half with the right sides facing each other, overlock (zigzag) the ends together.

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Fold the strips over to make a double layer tube.  This is the same as many of the cuffs I have sewn (e.g. Upcycled Merino Baby Pants).

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Pin over top of the trunks leg opening with all the raw edges together.

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It is nice to have the seams line up but I find that the thickness of the layers all together can be a bit much for the overlocker to handle.  So I stagger the seams so they are next to each other.

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With the pins in place I flip the trunks inside out as I find it easier to sew on the inside of the leg opening.

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Here you can see what I mean by sewing in the inside of the leg opening.  Take extra care to catch all the layers.

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And here they are, and yes again I am going topstitch them!  Yes it’s optional and you don’t have to at all but I really really like the seams staying put.  And remember you can use a matching or contrast thread colour.

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Step 7 – Waistband

Cut your elastic to size and zigzag the ends together (check out Joining Elastic here)

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Pin into the inside of your waist, taking care to spread the gather with a little more gather at the back than the front.

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I used the overlocker to attach the elastic but you can zigzag if you prefer.  Just sew right on the top edge and make sure you catch both layers.

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Fold over the waistband and pin in place.

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Zigzag on top of the seam you used to join the elastic, stretching gently as you go to keep the fabric smooth.

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Now just a few more shots of them in action!  He wouldn’t take them off said they were nice and comfortable and wore them for the rest of the day.  Best reward for a sewing Mum ♥

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4 thoughts on “Boys Swim Trunks (or underwear!) Pattern and Tutorial

  1. These look fantastic and so easy to understand your instructions
    I've not heard of scuba before – is it the same as neoprene?

  2. Hi Linda, Thanks for your lovely comment! I had never seen anything like the 'Scuba' fabric before, it is not neoprene it is thicker than normal swimwear fabric and is 95% Polyester and 5% Spandex. I hope that helps!

  3. Great tutorial Nina! I have some scuba material I got from spotlight in their remnant bin…it would be the perfect weight for this project!

  4. Thanks Hootnz! It works perfectly for togs, the kids have been wearing them daily for over a week now and the fabric is holding up well. I have made a pair of leggings out of the Scuba fabric and they pilled a lot. But it is nice and thick and definitely didn't need lining. I would love to see your project!

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