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Circle skirt maths - explained!


∏ = 3.141592653589793238462...

How many times in Maths class did/do you ever wonder when in the hell you'd actually need to know equations like this in real life? Well, to my dismay, it turns out that when you like to make stuff, Maths is kind of fundamental. Especially when it comes to making circle skirts. One of the easiest and quickest garments you can whip up on your machine, provided you can first figure out the radius of your waistline circumference... Ugh. Fear not, my mathematically challenged friends - we have figured it out for you. And made some pretty skirts along the way!

***Update - we made an app! Now you can leave the pesky sums to us and concentrate on the best part - sewing!***

Ready class? Then let's begin.

We're going back to GCSE Maths here guys. Remember pi?? That crazy 3 with endless decimal places is what we need to figure out the radius of our waistline circumferences. And why exactly do we need to know the radius? We need the radius in order to measure, mark out and cut the perfect little circle -that will be our waistline- onto the fabric. Without the radius, the only way to mark out the curve would be by shaping your measuring tape into a quarter circle on your folded piece of fabric (this ad hoc method I wouldn't even suggest to lazy stitchers as the results would inevitably be inaccurate, leading to a whole lot of time consuming fixing and tweaking and hair pulling and fabric wasted...).

For each type of circle skirt, be it full circle, half circle or quarter circle, the mathematical equation we need in order to find out the radius will be slightly different. Before we look at each one individually, we first need to know the foundation equation: Circumference (c) + two lots of seam allowance (3.2cm) ÷ ∏ (3.14) = diameter (radius × 2). We'd also like to point out now that we will be using metric measurements ie. centimetres, not inches. Nothing against Imperial, only that our brains simply can't cope with Imperial decimals, what with them being in eighths as opposed to tens...!

A note about seam allowance: seam allowance needs to be added on to both your waistline seam and side seams. For the waistline, we will be subtracting 1.6cm from your final radius measurement. For the side seams, we add 1.6cm for each raw edge to be seamed to your initial waistline circumference measurement: half and quarter circle skirts will have only one back seam so add 3.2cm to your waistline; a full circle skirt cut from 2 pieces will have 2 side seams so add 6cm altogether).

Full circle skirt

Let us begin by pointing out that it is unlikely you will be able to cut a whole circle skirt from a standard piece of 45" width fabric (unless making a miniskirt). The following diagram assumes that you will be cutting 2 semi-circles and joining them at the side seams, with your zipper inserted into one of those side seams - please see our invisible zipper tutorial when you get to that part!

Example: Your waistline measures 66cm (equivalent of a 26" waist). You are making a full circle skirt from 2 semi circles so you need to factor in the 4 raw edges that will be your 2 side seams. 66cm (C) + 6.4cm (4SA) = 72.4cm. 72.4cm ÷ 3.14 =  23cm (diameter). (23cm ÷ 2) - 1.6cm (waistline seam allowance) = 9.9cm (radius).

Tip: cut a piece of string the length of your final radius measurement and holding one end at the corner, use it to accurately mark out your curve.

Half circle skirt

Our waistline measurement now becomes a semi-circle, so in order to find the radius with our little equation we need to double the waist measurement.

Example: (66cm x 2) = 132cm (2C) + 3.2cm (2SA) ÷ 3.14 = 43cm (diameter). (43 ÷ 2) - 1.6cm (SA) = 19.9cm (radius).

Tip: before hemming your circle skirt it's a great idea to put it on a mannequin and leave it to "drop" overnight. Seeing as parts of a circle skirt hang on the bias, they'll need some time to stretch out naturally so you can then sew an even hem. If you don't give the fibres time to drop, you'll end up with a wavy, uneven hem line.

Quarter circle skirt

Just as we doubled the waistline as we halved the circle skirt, so we need to quadruple the waistline for a quarter circle skirt. The following diagram shows the quarter circle piece being cut from a single piece of fabric, no fold.

Example: (66cm x 4) + 3.2cm (2SA) = 267.2cm ÷ 3.14 = 85cm (diameter). (85 ÷ 2) - 1.6cm (SA) = 40.9cm (radius).

Phew... Broken out in a bit of a mental sweat there guys, and words like radius and circle have lost all meaning. We hope this has fully explained the maths behind constructing circle skirts and their variations - if not, let us know and we'll do our best to clarify anything further. We leave you with the pretty fruits of our experiments...and one final tip: hemming a curve can be tricky; try our rolled hem tutorial for a quick, slick finish!

Over and out x

Comments on this post (76)

  • Feb 08, 2021

    This is the most useful explanation I have ever read! Thank you so much!! You make it so straightforward!

    — Victoria

  • Dec 02, 2019

    Hi , thank you very much for the very clear explanation.

    — Sunny

  • Feb 05, 2019

    I would like to know about sleeves and how to measure and cut / thank you

    — Celestine Oneal

  • May 14, 2018

    Hi, Thanks for the wonderful tutorial. I love circle skirts but have only used them in a purchased patterns. I am happy I now have the opportunity to make my own from scratch , I want to start with the 1/4 circle for my 8 year old whose waist is 30". I used the app and it worked perfectly but I am unsure how many pieces to cut, I understand that the fabric should not be folded but do I cut out one or two pattern pieces to make the skirt.

    — Mimi

  • Feb 17, 2017

    Hi Lydia,

    Thanks! And no, we haven’t factored any ease into our calculations – that’s entirely up to you and your preference. The best thing to do is include your desired ease into your waistline measurement and then go ahead with the circle skirt calculator.

    Hope this helps!


    — Elisalex - By Hand London

  • Feb 17, 2017

    Hi Heather,

    To add a 1/4 circle skirt to the Anna bodice it’s simply a case of sewing the skirt to the bodice at the waistline – easy as pie!

    I hope this helps!


    — Elisalex - By Hand London

  • Feb 12, 2017

    Hi this is great. Any tips for adding a quarter circle skirt to an Anna bodice?

    — Heather

  • Feb 03, 2017

    I love your style! It’s sassy yet classy??? I was wondering if you factored any ease into the measurements calculated by your circle skirt calculator? If so, how much?

    — Lydia

  • Dec 09, 2016

    It always seems impossible until it’s done

    — Payday Loans

  • Aug 19, 2016

    Hi Bethany, the quarter circle is cut from just the one layer of fabric, however it can be tricky as the width of the fabric will prevent it from working after a certain waistline measurement, so you would probably have to cut your skirt from two panels to make up the quarter circle instead. I hope this helps! ~Elisalex

    — Elisalex - By Hand London

  • Aug 19, 2016

    Hi Elisa, you’ll need to add the extra 12" to your waistline measurement and calculate from there. I hope this helps! ~Elisalex

    — Elisalex - By Hand London

  • Aug 19, 2016

    Hi Catherine, yes – in order to make a full maxi circle skirt it will definitely need to be constructed from multiple panels. The easiest way to do this is draw out your full circle onto some pattern paper, and using our calculator to work out the radius, then simply draw out panels (maybe one big semi circle for the front piece and two quarters for the back, or four quarter panels – the amount of panels you need will depend on the width of your fabric), cut the panels out and add seam allowance to the new seams. I hope this helps! ~Elisalex

    — Elisalex - By Hand London

  • Jul 21, 2016

    Hey, I’m so happy to have come across your article. I’m in the process of designing an evening dress that has a full circle skirt. It is however very long and your calculator suggests to make something shorter. If I still want the full circle and the length do I just do a half circle and two quarters cut with no fold? I’m quite desperate at finding the right answer and your posts have come the closest to finding the answers. Please help!

    — Catherine

  • Jul 10, 2016

    if I’m adding 12 extra inches of fabric for a few pleats, would I still use the circumference of my waistline + seam allowance, or would I use circumference + seam allowance + 12 inches to find my radius? I’ve been scratching my head over this for a while maybe you can help! Thanks!!

    — Elisa

  • Jul 02, 2016

    Question about the quarter circle:
    Do you need to cut two pieces? The diagram for the app, and this post (both amazing helpful) shows only one, but for my 30" waist the piece only goes halfway round. I’m super new to the whole sewing thing, so any help would be greatly appreciated. Thanks!

    — Bethany Manuel

  • Mar 22, 2016

    Hello! Very good job(this site)! Thank you man.

    — JohnBush

  • Nov 06, 2015

    Hi, this looks like a great turtorial! I need to make a 1.5 circle or 3 half-circles skirt. How can I adapt the instructions for this?

    — Carola

  • Oct 30, 2015

    thank you… now am off to start my class project.

    — Raisa

  • Jul 14, 2015

    Hi ladies! Just gotten around to using this; great tutorial! It’s allowed me to come up with my own final equations which make just a little more sense to me.

    Just wanted to make a quick comment: for the full circle skirt, with four raw edges and thus two side seams, I guess you’re assuming the zip would be inserted in one of the side seams? For a back zipper, you’d need to add another 2SA to the waist measurement (and cut down one of the folded edges to create the back seam). If so, might be worth mentioning this assumption. Unless I’ve missed something? Really hope not else my student loan was a waste!

    Thanks again!

    — Jen

  • May 28, 2015

    I want to make a 3/4 skirt. Can you please help me find the radius? Thank you very much.

    — Honey

  • Nov 14, 2014

    Thank you so much for the app! I’ve used it a few times now and love it. I’m just wondering if it is necessary to double the waist measurement on the half cirle skirt as its divided by 2 at the end. I’m terrible at maths so sorry if the answrr is obvious!

    — Jade

  • Sep 01, 2014


    Great circle skirt tutorial! Can I make a small feedback though?

    I believe you need to add 1.5 cm waist seam to the Fabric Length Required. By your current app calculation, the final skirt length will be 1.5 cm shorter than what is intended. Just thought I’d let you know about this.

    — Tania

  • Jul 12, 2014

    hi there! :) it’s a great tutorial but i want ask about the hem and seam allowance that will add with the skirt length. What is suitable measurement of hem and seam allowance i should add on? thank you! :D

    — Faatihah

  • Jun 10, 2014

    Love the app but can I ask is there a way of adding in the variable of your height? Or waist to floor length…I’m only 5ft1 and I’m wondering if maxi will be too long.

    — LadyD

  • Jun 09, 2014

    Hi Nimsay, we’re definitely due an update of the app so we’ll be sure to include your suggestion – thank you! x

    — Elisalex - By Hand London

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