Most formal dress problems are never really about the dress. They're about size and colour — the two things you can actually control before you order. Get those right and the rest is mostly easy. That's what this guide is for.
1. Start with your measurements, not the label
Here's the thing nobody says out loud: dress sizes are not standard. A size 10 from one brand can fit completely differently to a size 10 from another, because every label grades its patterns its own way. So the first rule for anyone shopping for purple formal dresses Australia online is simple — ignore what you think you wear, and work from the numbers on a tape measure.
How to measure yourself properly
Stand in front of a mirror in your underwear or something close-fitting, and use a soft measuring tape. Three measurements are all you need:
- Bust. Wrap the tape around the fullest part of your chest, keeping it level across your back and under your arms. Not too tight, not loose — it should sit against your skin.
- Waist. Measure the narrowest part of your torso, usually a couple of centimetres above your belly button. Breathe out normally and don't pull the tape in.
- Hips. Measure the fullest part of your hips and bottom, keeping the tape parallel to the floor.
Write those three numbers down. You'll use them every single time you buy a dress, so it's worth doing once properly.
Every sizing system, side by side
Formal dresses are sold in at least four different size systems, plus the letter sizes. Here's how they line up. Note that these are typical ranges, not guarantees — different brands shift them, which is exactly why the measurements matter more than the number.
| Letter | AU / UK | US | EU | Bust (cm) | Waist (cm) | Hips (cm) |
|---|---|---|---|---|---|---|
| XS | 6 | 2 | 34 | 78–81 | 59–62 | 84–87 |
| S | 8 | 4 | 36 | 82–85 | 63–66 | 88–91 |
| M | 10 | 6 | 38 | 86–89 | 67–70 | 92–95 |
| L | 12 | 8 | 40 | 90–93 | 71–74 | 96–99 |
| XL | 14 | 10 | 42 | 94–97 | 75–78 | 100–103 |
| 2XL | 16 | 12 | 44 | 98–101 | 79–82 | 104–107 |
| 3XL | 18 | 14 | 46 | 102–105 | 83–86 | 108–111 |
| 4XL | 20 | 16 | 48 | 106–109 | 87–90 | 112–115 |
| 5XL | 22 | 18 | 50 | 110–113 | 91–94 | 116–119 |
| 6XL | 24 | 20 | 52 | 114–117 | 95–98 | 120–123 |
| 7XL | 26 | 22 | 54 | 118–121 | 99–102 | 124–127 |
Find the row where your own bust, waist and hip measurements all sit. That's your starting size. The letter and the number on the tag are just labels — your measurements are the only thing that's true about you.
When you land between sizes
Most people land between two rows, and there's a sensible way to choose. Size up if the dress has a fitted bodice or no stretch — taking a dress in is easy for a tailor, but letting it out is limited by the seam allowance. Size down only if the dress is generously cut and you're between sizes at the looser end. When in doubt, the bigger size is the safer bet, especially for a one-off event where you can't return it.
2. Order a swatch before you commit to the colour
Colour is where online ordering usually goes wrong, and it's almost never the dress's fault. Screens render colours differently — your phone, your laptop and your desktop monitor each display the same fabric as a slightly different shade, depending on calibration, brightness and even the time of day. A purple that looks soft and muted in a listing photo can arrive looking warmer, cooler or deeper than you expected.
That's why, if colour matters to you — and for a formal it usually does — you order the swatch first.
A fabric swatch is a small piece of the exact material used for the dress. You hold it in real light, hold it next to your shoes and accessories, hold it up against your skin tone, and you confirm the shade you're actually after. Only then do you place the order. It costs very little and takes a few days, and it saves the kind of disappointment a rushed purchase can't be walked back from.
This matters even more for a specific shade. Purple formal dresses Australia buyers usually want one very particular purple — the colour on the school formal palette, or the exact tone the bride picked from a photo. A screen can't guarantee that match. A swatch can, because you're judging the real fabric instead of a picture of it.
One honest note: even a photo of a swatch looks different on a screen. Judge the swatch itself, in daylight and in the room where you'll wear the dress, before you make the call.
3. What separates a good formal dress from a cheap one
Size and colour get you most of the way. The rest is construction, and you can check a few things without being a sewing expert:
- The fabric. Look at what it's actually made of and whether it has any stretch. A dress with a little give is far more forgiving on the night.
- The bodice. Formal dresses should be structured enough to hold their shape — boning or a good lining makes a world of difference to how it sits on your body.
- The zip. A cheap, flimsy zip can ruin an otherwise lovely dress. Check the zipper runs smoothly and feels solid.
- The seam allowance. Look inside at how much extra fabric is left at the seams. More allowance means an easier, cheaper alteration.
- The lining. A fully lined dress drapes better and feels more substantial than one that's just a single layer.
4. Leave time for the things you can't rush
Order well before your event. Even a perfect dress needs a fitting, and you want room for alterations, not just shipping. As a rough rule, give yourself at least a few weeks between ordering and the formal — swatch first, order, then alter.
Q&A
What size should I order if I'm between two sizes?
Size up. A tailor can take a dress in, but there's only so much fabric to let out.
Will the purple look exactly like the photo on my phone?
Probably not exactly. Screens vary, so treat any photo as an approximation and use a swatch to confirm the real shade.
How do I know if a dress will need alterations?
Measure yourself, compare against the size chart, and expect the hem to need work. Length is the most common alteration on formal dresses.
What if I need a slightly different shade?
Check what colours the brand actually offers and request a swatch before ordering. Purple ranges from barely-there lilac to deep aubergine, and the difference between them is exactly what a swatch sorts out.
The short version
Measure yourself first and trust those numbers over any tag. Order a swatch before the dress if the colour has to be right. Check the construction. Leave time for alterations. Most of what goes wrong with a formal dress was avoidable before anyone clicked buy — and now you know what to look for.
This guide comes from the team at zimmerformal, who make and fit formal dresses for Australian school formals, graduations and weddings. Every piece in the purple formal dresses Australia range is cut to the sizing chart above and available for swatch-first ordering, so the colour you confirm is the colour you get.
