How to Select Your Sewing Pattern Size
Choosing the right sewing pattern size shouldn't feel like guesswork. Unlike ready-to-wear clothing, where a size 12 in one shop fits completely differently from a size 12 in another, sewing patterns give you the power to create clothes that actually fit your unique body.
This guide will show you exactly how to choose your sewing pattern size, combine multiple sizes for a custom fit, and understand ease so your finished garments fit the way you want them to — not too tight, not too baggy, just right.
Why are sewing pattern sizes are different from shop-bought clothes?
Here's the thing: ready-to-wear sizing is chaos. A UK size 12 means something different in the US, varies between high street shops, and changes from one pattern company to another. We've all stood in a changing room surrounded by three different sizes of the same jeans, wondering which planet the sizing chart came from.
That's why Tilly and the Buttons patterns use numbered sizes (1, 2, 3 and so on) rather than the traditional 6, 8, 10... system. You'll see ready-to-wear sizes listed as a reference point, but they're secondary — the real magic happens when you ignore those numbers entirely and focus on actual body measurements instead.
When you sew your own clothes, you get to base your size on precise measurements and the finished garment dimensions, not arbitrary labels. Much better.
How do I know what my sewing pattern size is?
Step 1: Take your measurements accurately
Before you can choose your pattern size, you need to know your vital statistics. Grab a soft, flexible tape measure and ideally a full-length mirror (or at least one that shows your hips) so you can check the tape sits level all the way round.
What to wear: Your usual underwear — especially the bra you'll wear (if any) under the finished garment, as this affects your bust measurement. Or wear close-fitting clothes like leggings and a vest that don't add bulk.
The three key measurements:
- (Full) Bust — With your arms down and wearing your usual bra, measure around the fullest part of your bust (usually, but not always, in line with your nipples)
- Waist — Measure around the narrowest part of your waist or torso (where you bend at the side)
- Hips — Measure around the widest point of your hips and bottom
The crucial bit: Check in the mirror that your tape measure is parallel to the floor all the way around. A wonky tape = wonky measurements.
Depending on what you're making, you might also want to record your high bust (around your upper chest, under your armpits), sitting waist, sitting hip, bicep, or thigh measurements — but full bust, waist, and hip are your starting point for most patterns.
Step 2: Match your measurements to the size chart
Open up your pattern instructions and find the Find Your Pattern Size chart (it'll look something like the chart above in the Frida sewing pattern).
Now on the Body Measurements chart (highlighted under the turquoise column above) locate your bust, waist, and hip measurements on the chart. If you're between two sizes, you should usually choose the larger one — you can always take a garment in when you try it on, but letting it out is much harder.
Mistake to avoid: Don’t get the Body Measurements chart confused with the Finished Garment Measurements chart, or your garment will probably end up too small for you! (See the section on understanding ease below for more on this.)
A quick note on Tilly and the Buttons size ranges:
Since 2019, we've expanded our sewing pattern sizing to include 15 sizes from UK 6-34 or US 2-30. Sizes UK 16-34 are drafted, fitted, and graded separately for a curvier set of proportions, including more room at the full bust and waist.
While some of our older patterns are in a UK 6-20 range or a UK 6-24 range, our newer patterns as well as some of the most popular patterns from our back catalogue are in the full UK 6-34 range. The product description on each pattern will tell you which sizes are included.
Step 3: What if your measurements span different sizes?
Here's where it gets interesting — and where sewing your own clothes becomes genuinely life-changing.
Most of us don't fit neatly into one size across the bust, waist, and hips. Maybe you're a size 3 at the bust, size 5 at the waist, and size 7 at the hips. If that's you, welcome to being a normal human with a unique body shape.
In a shop, this means trying on seven different sizes and leaving empty-handed. When you're sewing, it means you get to combine pattern sizes to create a custom fit.
How do I combine sewing pattern sizes?
Each pattern piece has multiple size lines marked with numbers and different dash styles. To combine sizes:
- Draw a new line starting from the bust area on the line that matches your bust measurement
- Gradually blend to the line that matches your waist size in the waist area
- Continue blending to the line that matches your hip measurement in the hip area if needed
It's easier than it sounds — you're basically drawing a gentle curved line between the different sizes rather than abruptly jumping from one to another.
New to this? We have a detailed tutorial on how to combine pattern sizes that walks you through it step-by-step.
HOW TO COMBINE SEWING PATTERN SIZES
Top tip: Once you've worked out which lines you're cutting, trace over them in a coloured pen. This makes life so much easier when you're actually cutting out, especially if you're working from one of Tilly's books where the pattern pieces are layered on the paper sheets.
Understanding ease in sewing patterns
If you've ever wondered what the point of the Finished Garment Measurements chart is, this section is for you. Essentially this chart shows the size the actual garment will be once you’ve sewn it up.
You can subtract the measurements in the Body Measurements chart from those in the Finished Garment Measurements chart to see how much ease is included. Ease is the extra room added to a pattern beyond your body measurements. Even close-fitting garments need ease.
How much ease do you need?
For woven fabrics (non-stretchy), you’ll need a certain amount of wearing ease so you can breathe, move, and not split seams when you sit down. Typical minimum ease allowances are:
- Bust: 5-10cm (2-4in) — you need the most ease here so your lungs can expand
- Waist: 2.5-5cm (1-2in) — one inch keeps things comfortable, two inches leaves room for a big lunch
- Hips: 5cm (2in) — enough to sit, bend, and move without restriction
Beyond the wearing ease, some patterns, like the Lyra Shirt dress, include lots of design ease for an oversized, puffed, billowy or floaty style. Others, like the Noa Pinafore, are more fitted, with minimal ease included.
For stretch knit fabrics (such as jersey), a close-fitting pattern might even have "negative ease" — meaning the finished garment measurements are smaller than the body measurements. That's intentional. The fabric stretches to fit you closely.
Why this is useful: Once you understand ease, you may decide to size up or down based on how you like your clothes to fit. Just remember that sizing up or down affects the whole garment — shoulders, sleeves, armholes, everything – so proceed with caution.
When your measurements don't tell the whole story
Sometimes bust-waist-hip measurements aren't enough. Maybe you have narrow or broad shoulders, a longer or shorter torso, or a fuller or smaller.
That's when fitting adjustments come in.
Every Tilly and the Buttons pattern has a dedicated fitting guide that directs you to common adjustments specific to that design — things like shoulder adjustments, bust tweaks, and length changes. You'll find these in our sewalongs section under each individual pattern.
ALL SEWING PATTERN SEWALONGS + FITTING GUIDES
Common fitting adjustment tutorials
We've written in-depth tutorials for the most common fitting challenges people make when sewing. Here's some of what's covered in our Fitting Help guide:
- Full bust adjustments (FBA) and small bust adjustments (SBA) for adding or subtracing room at the bust
- Lengthening and shortening patterns for torso and limb length
- When to make a toile (test garment) before cutting into your good fabric
... and lots more!
VISIT THE COMPLETE FITTING HELP GUIDE
Want hands-on help with fitting?
If all this feels like a lot to figure out on your own, we get it. Fitting is one of the trickiest parts of sewing — but also one of the most rewarding once you crack it.
Our Bodice Fitting for Home Sewing online workshop takes you through the entire process of getting a great fit across the bust, waist, hips, neckline, shoulders, back and armholes. You'll learn how to identify fit issues, fix them, and transfer your changes back to your pattern.
LEARN MORE ABOUT BODICE FITTING FOR HOME SEWING
Your next steps
Now you know how to choose your sewing pattern size, here's what to do:
- Take your measurements (bust, waist, hips) wearing your usual underwear
- Match them to the Body Measurements size chart in your pattern instructions
- Check the ease to make sure the fit matches your preference
- Combine sizes if needed by blending between different size lines
- Make adjustments if your body proportions need tweaks beyond standard sizing
Remember: sewing your own clothes means you're in control. No more settling for "close enough" — you get to make garments that fit your actual body, not some mythical average person.
Now grab that pattern and get cutting. You've got this.
