How to Choose Your Size on a Sewing Pattern (Bust, Waist, Hip)

To choose your size on a sewing pattern, measure your bust, waist and hip over the underwear you will wear with the garment, compare the three numbers with the size chart on the pattern page in centimetres or inches, and pick the size by the measurement that matters for that garment: bust for tops and dresses, hip for trousers and most skirts. Your shop size plays no part in it. Pattern sizes describe the body, not the label, and the same person is often one or two sizes "bigger" on a pattern chart than on a shop rail. This guide goes through the three measurements, the cm-versus-inch question, and which measurement decides for each kind of garment, with examples from the Sewly catalog.

Why a pattern size is not a shop size

Shop sizes are set by each brand and drift over time. A pattern size is fixed to a set of body measurements printed next to it. On Sewly, every women's pattern uses the same chart, so you work out your size once and it holds across the whole catalog:

Size	Bust	Waist	Hips
XS	82.5 cm / 32.5 in	61 cm / 24.0 in	87.5 cm / 34.5 in
S	87.5 cm / 34.5 in	66 cm / 26.0 in	93 cm / 36.6 in
M	90 cm / 35.4 in	68.5 cm / 27.0 in	95 cm / 37.4 in
L	96.5 cm / 38.0 in	75 cm / 29.5 in	101.5 cm / 40.0 in
XL	104 cm / 41.0 in	82.5 cm / 32.5 in	109 cm / 42.9 in
2XL	114 cm / 44.9 in	93 cm / 36.6 in	119 cm / 46.8 in
3XL	126 cm / 49.6 in	110 cm / 43.3 in	132 cm / 52.0 in
4XL	140 cm / 55.1 in	124 cm / 48.8 in	146 cm / 57.5 in
5XL	148 cm / 58.3 in	135 cm / 53.2 in	156 cm / 61.4 in

Read the chart as a description of a body, not as a judgement. If your bust is 96 cm you are an L on this chart whatever label you buy in a shop, and the dress will fit because of it.

How to take the three measurements

Use a soft tape measure, stand naturally, and have someone help if you can; it is hard to keep a tape level around your own back.

1. Bust. Around the fullest part of the bust, with the tape level across the back and snug but not tight. Wear the bra you will wear with the garment. Breathe normally.
2. Waist. Around your natural waist, which is the narrowest point of your torso, usually a little above the navel. If you are not sure where it is, bend sideways; the crease is your waist. Tie a piece of string there and measure over the string.
3. Hip. Around the fullest part of your seat, usually 18 to 23 cm below the waist. Check in a mirror that the tape is level at the back, where it tends to drop.

Write all three down, in the unit you measured in, and measure twice. A difference of 2 cm at the bust is half a size.

Centimetres or inches

Sewly charts show both units, so measure in whichever your tape uses and compare in the same column. Do not convert unless you have to, and if you do, use 2.54 cm to the inch and keep the decimal: 37.5 inches is 95.3 cm, which is an M, not 95 rounded down to something else. The half-inch matters most on fitted garments and at the top of the size range, where the steps between sizes are larger.

The same applies when you print. The test square on the first page of a PDF pattern is 5 by 5 cm or 2 by 2 inches, and a square that is a few millimetres off means a garment that is a size off.

Which measurement decides

Once you have three numbers, they will often fall in two or three different sizes. The garment tells you which one to follow.

A fitted dress with a zipper. Choose by the bust, then check the waist and hip against the chart and adjust the side seams where they differ. Sleeveless Princess Seam V-Neck Fitted Dress is a good example: it is a woven dress with a back zipper and no stretch, so the size has to be right, but the princess seams give you four places to let out or take in a centimetre or two.

A fitted knit dress. Fitted Bodycon Pencil Dress with Square Neckline is drawn for stable knits such as ponte or a medium-weight jersey with good recovery. Choose by bust and hip together; if they disagree, follow the larger one at the hip and blend to the smaller at the bust. If you are between sizes everywhere, knits forgive the smaller size, wovens do not.

A loose dress without a waist seam. Choose by the bust alone. Relaxed Fit Linen Dress with Side Pockets skims from shoulder to hem, so there is nothing fitted below the bust for your waist or hip measurement to affect.

A skirt with a fitted waistband. Choose by the waist. A-Line Linen Midi Skirt with Pockets sits at the natural waist with gathers below it and an A-line that skims the hips, so the waistband is the only part that has to match a measurement.

Trousers with an elastic waist. Choose by the hip. Relaxed Linen Pants with Elastic Waistband and Pockets have to pass over your hip when you pull them on, and the elastic then takes the waist in to wherever it is.

Children's clothes. The size is labelled by age, but age is only a starting point. Girls Tiered Dress with Peter Pan Collar and Pockets, 2 to 10 Years lists height, chest and waist for each size: a 2Y is a height of 92 cm and a chest of 53 cm, a 12Y is 152 cm and 78 cm. Pick the size by the chest and adjust the length to the height.

Men's patterns follow the same logic: chest for shirts, hip for elastic-waist trousers, and the chart on the pattern page in both units.

Between two sizes

If a measurement falls between two sizes, you have three options, in order of preference.

1. Blend. Cut the larger size where the larger measurement is and the smaller size where the smaller one is, and draw a smooth line between them over 10 to 15 cm. On a dress this usually means the hip in one size and the bust in another.
2. Go larger on wovens. A fitted woven garment can be taken in at the seams; it cannot be let out beyond the seam allowance. If you cannot blend, cut the larger size.
3. Go smaller on stable knits. Knits stretch to the body, so the smaller size usually fits better and sits without wrinkles.

On Sewly, most patterns come as one file per size, so print both sizes you need and trace the blend from one onto the other. Where a pattern is a single layered file, turn on only the two layers you need before printing.

Ease: body measurements are not garment measurements

A size chart lists body measurements. The finished garment is larger than the body by an amount called ease, which is what lets you breathe, sit and raise your arms. A relaxed shift dress has a lot of it; a bodycon dress in a knit has almost none or less than none. That is why the pattern descriptions say things like "skims rather than clings": they are telling you how much ease to expect.

For a fitted woven dress, it is worth sewing the bodice once in cheap cotton before cutting the real fabric. It takes an hour and tells you whether to move a seam. For loose styles, skirts with gathers and anything with an elastic waist, go straight to the fabric.

Before you cut

Measure, pick the size by the measurement that decides, print, and measure the test square before you cut a single piece. How to Print a PDF Sewing Pattern at Home covers the printing side, including what to do when the square comes out the wrong size. Then browse the Sewly catalog or the patterns page; every pattern page has the full size chart under the description, in centimetres and inches.