Shirt to Romper

Trying to be frugal I saw a tutorial on making a shirt into a baby romper/onesie but found the pattern to be slightly lacking so here’s my version 😀

First Step

You will need:

Paper (I use lining paper)



Rubber/Eraser (just in case)


Footless babygro/romper or similar that fits

Shorts (if wish to do a shorter one)

I will be making a long sleeved full leg onesie & a short sleeved short leg version too.


Second Step

Lay your paper flat on a table. Fold your romper in half make sure outer edges & leg edges match so perfectly symmetrical or your pattern wont work. You need to do it at least 3 cm in from edge of paper. DO NOT trace this onto edge of paper like I did to start!!


Trace round this starting at armpit ending to outer shoulder. Photo below is maybe not massively clear but shows what you should end up with. Remember I did it at edge to start which is wrong. Mark bottom line with a big CF this stands for centre front.


To left of picture it shows 2 darker curved lines these are your neck lines the top is back & lower is front. To trace front keep romper on paper & just fold it the back under slightly so your able to then trace the front neck.


Next you need to draw in arm hole curve. Take the sleeve and pin it back along seam so reveals curve of arm when pinned.


Match up armpit & shoulder to pattern and finish the pattern off by tracing the curve of sleeve.


Third Step

Now you need to straighten the lines of pattern all but the neck & arm hole are straight. You then need to make 1cm from edge of pattern at outer edge (top of pattern if laid like mine) at neck & arm hole. Then 2cm at inner edge (CF), inside leg & at base of legs.

This is why you shouldn’t trace pattern at edge of paper. You will end up with a bordered pattern. The ‘border’ is your seam allowance.


Ensure you also mark 1cm for front neck line. Then mark where you want the opening of your shirt to end as this romper will have opening at front to about breast bone or where ever you wish. I marked 13cm from front neckline border.

Fourth Step

We will do sleeve pattern now.

Lay your sleeve flat on the paper and trace round shoulder to armpit.


Now we need the curve where the sleeve is sewn to the armhole of main section. As can see in picture above where armhole was curved in the sleeve curve goes out. The easiest way to do this is to draw a slight curve freehand as shown below.


Now like you did with other section add 1cm to all edges apart from cuffs add 2cm. Again this ‘border’ is your seam allowance. You should have both patterns as shown.


If you wish to do short version then follow next step otherwise skip to sixth step.

Fifth Step

Using the pair of shorts fold in half symmetrically like you did for the romper. Matching the crotch of trousers to your pattern crotch mark where the hem is.


Arrow shows shorts crotch & line is pattern crotch.

using line just draw add 2cm for seam allowance. Rub out first line.


Sixth Step

We will be drawing back of the pattern now. You can either pre fold your paper or do as I do and fold after.

Fold the 2cm seam allowance on the CF edge & inside leg in you wont need this.


Lay the romper pattern towards edge of paper with the CF edge towards middle of the paper & draw round. Fold at CF and cut around both pieces from top of neck right round to crotch. DO NOT cut along CF. You should end up with one big piece. This is the back of your pattern.


You now have a back, half a front & a sleeve. You can cut the back section of the neck off the front pattern piece as pic shows so the front piece has front neckline which is lower and back piece has the back neckline which is higher.


Last Step

We will need facings this means you don’t hem the neck line which makes it tidier.

To make these fold your back piece in half lay on a fresh piece of paper & trace round starting 10cm from armpit round to other side.


Do same for front. Clearly mark each piece.

EDIT: I’ve found since I made this that you need a gusset patch this goes between the legs by the bum and allows space for nappies. I didn’t do this but using same methods above you can get dimensions off a well fitting romper or trousers.

Another thing to consider if the romper I use was stretch material so if you want a baggy look add more seam allowance.

Next time we will cut the romper out from our shirt & sew it up.

For this you will need:

Old shirt (bigger the better)


Your pattern



Popper tape

Bias binding that coordinates with your shirt


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