Sewing Pattern Size Picker
A shop size 10 is a pattern size 16. Choose a top by high bust, not full bust — going by full bust can be two sizes too big in the shoulders.
Where you land on the chart
A pattern size is not a shop size
Pattern companies still use body measurements standardised in the 1970s. Ready-to-wear drifted away from them for decades through vanity sizing, so the same body is a much larger number on a pattern envelope than on a shop label. People buy their shop size, cut it out, and produce something enormous.
| Shop size (roughly) | Pattern size | Gap |
|---|---|---|
| 2 | 10 | 8 sizes |
| 4 | 12 | 8 sizes |
| 6 | 14 | 8 sizes |
| 8 | 14 | 6 sizes |
| 10 | 16 | 6 sizes |
| 12 | 18 | 6 sizes |
| 14 | 20 | 6 sizes |
| 16 | 22 | 6 sizes |
Treat that table as an illustration, not a conversion. Shop sizes are not standardised between brands or over time — that is the entire reason the gap exists — so no table can map them reliably. The only method that works is to ignore the number completely and use your measurements, which is what the calculator above does.
Choose a top by high bust, not full bust
Patterns are drafted for a B cup — a two-inch difference between the measurement above your bust and the one across it. So the chart's bust column is the full bust of that standard body, and the size drafted for your frame is the one whose chart bust equals your high bust plus two inches.
| High bust | Full bust | Cup | By frame | By full bust | Bust adjustment |
|---|---|---|---|---|---|
| 32″ | 34″ | B | 12 | 12 | none |
| 32″ | 35″ | C | 12 | 14 (1 too big) | +1.0″ |
| 32″ | 36″ | D | 12 | 14 (1 too big) | +2.0″ |
| 32″ | 37″ | DD | 12 | 16 (2 too big) | +3.0″ |
| 32″ | 38″ | F | 12 | 16 (2 too big) | +4.0″ |
Notice the first row: a B cup needs no adjustment at all, because that is the body the pattern was drafted for. That is the check the rule has to pass, and any rule that gives a B cup something to adjust is the wrong rule.
Going by full bust instead buys a size drafted for a bigger frame. At four inches of difference that is one size too big through the shoulders, neck and armholes; at six inches it is two sizes. Those are the parts of a garment that cannot be taken in afterwards without redrafting, which is why the size goes by the frame and the extra room goes in at the bust where it is needed.
The finished garment is always bigger than you
The chart lists body measurements. The garment has ease added on top — some of it just so you can move, the rest of it styling. Measuring a pattern piece, seeing spare inches and cutting a size down removes the room you need to sit down in.
| Envelope says | Ease at the bust | A 34″ body finishes at | |
|---|---|---|---|
| Close-fitting | 0–2.875″ | 34.0–36.9″ | Knits and stretch wovens only. A woven at zero ease will not let you raise your arms. |
| Fitted | 3–4″ | 37.0–38.0″ | A tailored dress or a fitted blouse. |
| Semi-fitted | 4.125–5″ | 38.1–39.0″ | Shaped but not tight. The commonest. |
| Loose-fitting | 5.125–8″ | 39.1–42.0″ | A relaxed shirt or an unstructured jacket. |
| Very loose-fitting | 8–12″ | 42.0–46.0″ | Oversized coats and outerwear worn over layers. |
Before any styling at all, you need about 2.5″ at the bust, 0.5″ at the waist and 2″ at the hip simply to move and breathe. That is why "close-fitting" starts at zero only for knits — a woven garment at zero ease will not let you raise your arms.
Almost nobody is one size
Bust, waist and hip routinely land on three different sizes. That is the normal case rather than a defect in you or the pattern, and the answer is to blend — cut the bust at one size, the waist at another, and draw a smooth line between them along the seamline. Multi-size patterns print every line for exactly this reason. Picking one size and hoping is what produces a garment that fits in one place.
- Measure over the underwear you will wear with it, snugly, without pulling the tape tight. Get someone else to do it if you can — measuring your own back is where most of the error comes from.
- Skirts and trousers go by hip, not waist, because a waist is far easier to alter than a hip.
- Make a muslin for anything fitted. It is the only way to find out what your measurements did not tell you, and it costs a few dollars of cheap fabric.
How to use
- Measure over the underwear you will wear, snugly and not tight.
- Choose the size by high bust, then adjust at the bust itself.
- Blend between sizes rather than picking one and hoping.
- Make a muslin for anything fitted before cutting good fabric.
Frequently asked questions
Why is my sewing pattern size so much bigger than my shop size?
Because pattern companies still use body measurements standardised in the 1970s, while ready-to-wear drifted away from them for decades through vanity sizing. A body that buys a shop size 10 is roughly a pattern size 16. Nothing is wrong with you or the pattern — the two numbers simply measure different things.
Can I convert my shop size to a pattern size?
Not reliably, and that is the point. Shop sizes are not standardised between brands or even between seasons at the same brand, which is exactly why the gap exists in the first place. Any conversion table is an illustration rather than an instruction. Use your measurements and ignore both numbers.
What is the high bust measurement?
It is taken above the bust and under the arms, across the top of the chest. It measures your frame — shoulders, upper chest and back — rather than your bust, and for choosing a pattern size it is far more useful than the full bust, because the frame is the part that cannot easily be altered afterwards.
Why choose a pattern size by high bust?
Because patterns are drafted for a B cup, meaning a two-inch difference between high bust and full bust. The chart bust column is the full bust of that standard body, so the size drafted for your frame is the one whose chart bust equals your high bust plus two inches. Choosing by full bust instead buys a size drafted for a bigger frame entirely.
How wrong does going by full bust get?
At a four-inch difference between high and full bust it is one size too big through the shoulders, neck and armholes. At six inches it is two sizes. Those are the parts of a garment that cannot be taken in afterwards without redrafting, whereas adding room at the bust is a standard adjustment.
What is a full bust adjustment?
Adding width and length at the bust of a pattern piece without changing the shoulders, neck or armhole. The amount is your full bust minus the chart bust of the size you chose by high bust. For a B cup that comes out at zero, which is the check any correct version of the rule has to pass.
Does the pattern cup letter match my bra size?
No, and treating them as the same causes a lot of confusion. Bra cup letters are the difference between your bust and your underbust; the pattern equivalent is the difference between your full bust and your HIGH bust, measured above the bust rather than below it. They are different measurements and routinely give different letters.
Why is the finished garment bigger than the size chart says?
Because the chart lists body measurements and the garment has ease added on top. Some of it is wearing ease, so you can move at all — about two and a half inches at the bust. The rest is design ease, which is the styling. A fitted dress in a 34 inch size finishes around 37 to 38 inches, entirely on purpose.
Should I size down if the pattern measures bigger than me?
Almost never. That spare width is the ease you need to sit, reach and breathe, and removing it is how a garment ends up unwearable. Check the finished garment measurements printed on the pattern piece against a garment you already own and like, rather than against your body.
What do fitted, semi-fitted and loose actually mean?
They are ranges of total ease at the bust. Close-fitting is under about 3 inches and really only works in knits; fitted is 3 to 4; semi-fitted 4 to 5; loose-fitting 5 to 8; very loose above that. The envelope prints the word and this page prints the inches it stands for.
My measurements are three different sizes. Which do I pick?
None of them — blend. Cut the bust at one size, the waist at another, and draw a smooth line between them along the seamline. Multi-size patterns print every line for exactly this reason. Landing on three sizes is the normal case rather than a defect, and picking one produces a garment that fits in one place.
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