Thursday, 23 January 2014

Crafty Maths - Full Circle Skirt Tutorial - Part 1

Full circle skirts are great to look at and fun to wear. Whenever I see a poodle or rock’n’roll skirt from the 1950s I just want to bop around singing Hand Jive from Grease - which probably isn’t wise given my limited vocal ability and general lack of exercise. But they sure make me smile

I love making full circle skirts - they are very useful as a base for all sorts of dance and theatre costumes - here are some lycra skirts I made for the Who characters in a production of Seussical the Musical my children were in last year. 

The younger cast members especially loved twirling round in them which got me thinking I should run up some elasticated waist ones for my nieces in time for the summer.

Full circle skirts are “exactly what it says on the tin”. They are made from a circle of fabric. But with a hole in the middle. Sounds easy I thought, but there was a bit of trial and error to get them to look right. I don’t usually work from patterns - I make it up as I go along - so I folded my fabric into 4 and cut what I thought were quarter circle shapes by eye. Not good - my first attempts were really lopsided - with a very uneven hem. I also messed up the hole in the middle - more oval than circular and usually too big or two small around the waist. So I thought it best to work out a pattern.

It all comes down to maths - circles, arcs, radius and circumference. If this is music to your ears you’ll enjoy working it out for yourself - but if you’d rather someone else does the calculations, I’ve added a few ready worked out at the end.

So back to my school days - the circumference of a circle is the measurement all the way round the outside - the blue line in my diagram. And the radius is the distance from the middle to the outside - the red line.

And there is a nifty little formula which says the circumference of a circle is twice the radius multiplied by something called “Pi” - a number just a little bigger than 3.

(To be precise pi is 3.14159265359 plus a load more numbers at the end but we won’t go there..)

I used this formula to work out a pattern for my skirt. Imagine your finished full circle skirt is laid out flat on the floor - it will look like a doughnut. Or a polo mint. But try to think of it as two circles laid on top of each other.

For my elasticated skirt, the size of the smaller circle (the hole) is based the circumference - the blue circular line - being the same as the measurement around the widest part of your child’s lower body - the hip measurement. Work in cm as it makes the calculations easier. Honest.

My niece has a hip measurement of 70cm, 
so the circumference of the hole needs to be 70cm. 

You may be tempted to add a little to the hip measurement so your child can get it on easily. But wait. You will find that no matter how carefully you work out the maths, the hole will always be a bit bigger than you expect because of something called bias which means the fabric will stretch, plus you will make the hole bigger when adding the waistband as you'll lose the sean allowance. (When I was working in really stretchy fabric like lycra I found I actually needed to reduce the size of the diameter. It is always easier to err on the small side as you can always make the hole bigger but you can’t add any back on.)

Next you need to calculate the radius of both circles - the two red lines. So let’s do the short one first. Remember the formula I mentioned early - well if we turn it around we can use it to calculate the length of the line. So the radius = circumference divided by 2 times pi. To keep the maths simple, I cut pi back to 3.14 so 2 times pi = 6.28. So just divide your hip measurement by 6.28 to find out the length of the short red line.

In my example the short red line = 70/6.28 
which is about 11.1cm. 

Although it is tempting, avoid rounding the answer to full centimetres. It is best to round to 1 decimal place as you can easily read millimetres on your tape measure and a few extra millimetres here can make a huge difference to the size of the hole.

The length of the longer red line is really easy - just add the length of the short line to the length you want your skirt to be. I wanted mine to be about 32cm - just above her knee.

So for my skirt the long red line = 11.1 + 32
which is 43.1cm. 

You can round the long red line to the nearest half centimetre if you like - it just determines the length of the skirt so a few mm each way doesn’t make a huge difference here. So I am going to use 43 cm.

Ok. We have the numbers. How do you use them? While it is possibly to lay out paper (or fabric) flat and draw full circles, I find it much easier to create a pattern for just a quarter of the skirt. Take a piece of paper which has at least one square corner. I like patterned paper as it is a good size and has grid lines that make checking the square easier, but you can also tape sheets of drawing paper or newspaper together.

Tape the paper down so it doesn’t move and push a pin into the square corner - it works best on low pile carpet or an old table - don’t ruin your family heirloom or polished floors.

Attach one end of a piece of string to the pin and tie the other end to a pencil near the point. When the pencil is held perfectly vertical, the distance between the pin and the point of the pencil needs to be the length of the longer red line - in my case 43cm.

Making sure the pin and paper don’t move and keeping the string taut, draw a curved line (an arc) with the pencil - this is the bottom of your skirt.

Cut the string shorter and retie to the pencil to the length of the shorter red line - in my case 11.1cm. Draw another arc in the same way - this is the top of your skirt.

It is really important to check the accuracy of these arcs - use a tape measure to measure from the pin to the drawn lines in a number of places - if your pencil doesn’t stay perfectly vertical the line will wobble - resulting in oval waistbands and wonky hems.

Once you are happy with your pattern, cut it out. You won’t need to add any allowances - adding the waistband compensates for length lost in seams and hems.

Fold your fabric into half and then in half again - ironing creases if possible to make sure the folds are precisely square. Place your quarter pattern on the folded fabric, making sure the smaller hole is towards the folded centre of the fabric not the open end.

Move the pattern up or down to line it up so that both the straight lines of the pattern are against the folded edges of the fabric.

Pin and cut along the curved edges of the pattern only - don’t cut along the straight lines.

And there you have it! When you open out your fabric you should have a perfect doughnut.

You may want to check it fits your child before finishing. It should fit over the hips easily - if it is a little too small, refold into quarters following the ironed creases, pin and cut a little off the top of the fabric following the cut line as a guide. If it is a little too big - don’t worry - it will just be more gathered around the waist.  

Simple. Now you need to do to finish it is add an elasticated waistband and hem it. Look out for another post from me soon - where I’ll show you how I finished some of the circular skirts I made.


The Old Button Full Circle Skirt - Radius Ready Reckoner
(all measurements in cm).



  1. Have the crafty challenges finished here now?

  2. No they will be restarting soon :)


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