The Ultimate Bra Fit Guide: Find Your True Size at Home

Being a woman, the best part of your day shouldn’t be ripping off your bra the second you walk through the door.

If it’s the only time you feel like you can finally breathe, it’s usually a sign your bra isn’t fitting the way it should.

Well, you aren't alone in this struggle. According to data supported by The New York Times, around 8 out of 10 women are wearing the wrong bra size… Most of us were told a size once, stuck with it for years, and then assumed that digging straps, restricted ribs, spillage, or an unsupported feeling was normal.

They’re not.

A well-fitting bra should feel secure and supportive without constantly reminding you it’s there. It should sit where it’s meant to sit, stay there, and make your clothes look smoother—without feeling restrictive.

This guide will help you find your bra size at home in just a few minutes, then walk you through a simple fit check so you can shop with confidence.

Table of Contents

1. Bra Size Calculator (Start Here)
2. Moving Past The Plus 4 Myth
3. How to Get Your Real Numbers (Band + Bust)
4. The Calculation (How Cup Sizes Work)
5. UK Bra Size Chart (Quick Reference)
6. Bra Size Conversion (UK ↔ US ↔ EU)
7. Sister Sizes (The easiest “close-but-not-perfect” fix)
8. Common Fit Problems (and what they usually mean)
9. The Best Bras for All Functions (Conturve Picks)
10. How to Make Sure Your Bra Size Is Correct (60-second fit check)
11. Best Bra Types for My Shape
12. Expert Q&A
13. Care Guide (so your bras keep their lift)

Bra Size Calculator

Before you overthink anything, start with our bra size calculator.

It gives you a clear starting point in seconds—as long as your measurements are taken correctly (we’ll walk through that next). If your result feels close but not perfect later, don’t worry—that’s completely normal. Your result will include sister sizes so you can adjust until it feels right without guessing.

Moving Past The Plus 4 Myth

You don’t need a professional fitting room to find your best fit—you can absolutely do it at home.

But first, let’s clear up an old myth.

Many of us were taught the “Plus 4” method: measure your ribcage and add four or five inches to get your band size. That method made sense decades ago, when bras were made from rigid fabrics.

Modern bras are designed with stretch and recovery. Adding inches often leaves you with a band that’s too loose to do its job.

Your band should sit snugly against your ribcage—that’s what anchors the support. When it’s too loose, the bra shifts, straps start digging, cups gape, and you find yourself adjusting all day.

How to Get Your Real Numbers

This part is simple. You just need to measure carefully.

Most sizing mistakes happen because the tape is too loose, too tight, or angled unevenly across the back.

Quick tip: Measure in a non-padded bra (or no bra). Keep the tape level in the mirror.

The Band (Support)

Start with your underbust, because this becomes your band—and the band provides most of your support.

Wrap the tape right under your bust, keep it level all the way around, and pull it snug. Not painfully tight—just secure.

If you’re measuring in inches and land on an odd number, you’ll usually round up to the nearest even band size (for example, 33" typically goes to a 34 band).

The Bust (Volume)

Now measure around the fullest part of your bust. Keep the tape level and avoid compressing the tissue—you want the natural measurement.

If you take these two measurements carefully, congrats, you’ve already avoided the most common sizing mistakes.

The Calculation (How Cup Sizes Work)

The band reflects your ribcage measurement.
The cup reflects the difference between your bust measurement and your band measurement.

In simple terms:

Cup Size = Bust Measurement − Band Size

Each inch of difference usually corresponds to one cup step (A, B, C, D, and so on).

One thing that clears up a lot of confusion: cup letters aren’t fixed volumes. A 32D and a 38D are not the same “D.” The cup volume changes with the band.

If you don’t want to do any maths, skip this part—the bra size calculator does it for you.

Conturve UK Bra Size Chart

Your bra size calculator will do the work for you, but it helps to have a quick reference chart on the page, especially for readers who want to sanity-check their numbers.

Bra Size Conversion (UK ↔ US ↔ EU)

If you’ve ever ordered from a different brand and thought, “Wait… am I suddenly a totally different size?”

Well, you’re not imagining it. Sizing labels vary by region.

Sister Sizes (The Close-But-Not-Perfect Fix)

If your calculator result feels almost right, sister sizing is usually the answer.

It lets you adjust the band without dramatically changing cup volume.

Here’s the rule:
Down a band = up a cup.
Up a band = down a cup

For example: If you wear 34D, your sister sizes are 32DD (tighter band) and 36C (looser band).

Sister sizing is especially helpful if your band rides up, your straps dig in, or your cups feel nearly right but not quite.

Common Fit Problems

If something feels off, it’s usually a predictable sizing signal.

If your band rides up your back, it’s typically too big. A band that isn’t anchored can’t provide stable support, which is why it shifts upward as you move. In most cases, going down a band (while adjusting the cup using sister sizing) solves it.

If you’re spilling out at the top or sides, your cup is likely too small—or the style doesn’t offer enough coverage for your shape. Sizing up in the cup often fixes it quickly.

If your cups gape or wrinkle, don’t assume you measured incorrectly. Gaping can mean the cup is slightly too big—but it can also happen when the band is too loose and the cups aren’t sitting flush. This is why trying the tighter sister size first often makes more sense than jumping straight to a different cup.

Two other common issues (especially after 40):

If your straps slip or dig in, the band isn’t snug enough—try the tighter sister size before blaming your shoulders.

If you’re slipping out underneath (“underboob escape”), the band may be too loose, or the cup shape may not contain you properly.—size down in the band or try a more secure, fuller coverage cut.

The Best Bras for All Functions (Conturve Picks)

Once your size is right, the next step is choosing the bra that fits your day—not just your measurements.

For everyday wear—when you want coverage that sits flush (so you’re not dealing with gaping or side spillage), and a smooth look under tops—the Ultimate Comfort Wireless Support Bra is the easy go-to.

Best for: smooth coverage under tops, everyday lift, and a secure feel without wires.

For strapless outfits and tricky necklines—when you want a clean neckline and a smooth silhouette without worrying about the bra showing—the Convertible Strapless Bandeau Bra is designed to stay put and keep lines minimal under fitted clothes.

Best for: strapless looks, clean edges, and fewer “pull it up” moments.

If you prefer a more adjustable, shaping fee—especially if you sit across a wider cup range or you’re often between sizes—the Adjustable Wire Free Shaper Bra lets you fine-tune your fit while staying wire-free.

Best for: dialling in coverage, reducing gaping/spilling, and a more held-in shape.

The goal isn’t just a bra that “technically fits.” It’s a bra you don’t think about all day.

The 60-Second Fit Check

Now we confirm everything, because this is what stops returns and guesswork.

Stand in front of a mirror and check three things:

First, your band should sit level and feel secure on the loosest hook (for a new bra).

Next, your cups should look smooth—no gaping, no bulging, no tissue escaping at the sides.

Finally, straps should sit comfortably without digging in, because the band should be doing most of the support.

Then do a quick movement check: lift your arms, twist slightly, take a deep breath. The bra should stay in place without you needing to adjust it.

Best Bra Types for My Shape

Even in the correct size, the wrong style can feel “off.” That doesn’t mean you’re hard to fit—it means the bra shape doesn’t match your shape.

If you often get top gaping, you may prefer styles with more secure cup edges or slightly more coverage.

If you often get top spillage, you’ll usually feel better in a more containing cut rather than a very low plunge. If you need a bra to disappear under tight tops, seamless T-shirt styles help keep lines minimal.

Quick Tip: If you fluctuate month to month, adjustable styles (or keeping two sister sizes) can save you a lot of frustration.

 

Expert Q&A

What if the bra size calculator gives me a size that feels tight?
A new bra should feel snug on the loosest hook. If breathing feels restricted or the band painfully digs in, try the sister size up (looser band).

What if my size changes throughout the month?
That’s common. Many women keep two close sizes (or sister sizes) for different weeks.

Why do my straps dig in even when the cups feel fine?
Usually, the band is too loose, sothe straps take the load. Try the tighter sister size before tightening straps further.

Why do my cups gape when I sit but not when I stand?
It can be a shape/style mismatch. Try a different cup shape or slightly different size, then confirm with the fit check.

Why do I spill out at the top but the cup feels “big enough”?
Often, the style is too open (like a plunge) for your shape. Try fuller coverage or size up a cup.

How often should I re-measure?
If your weight changes after pregnancy, or if your bras suddenly feel off. Otherwise, every 6–12 months is a sensible check.

How do I know if I should change the band or the cup?
If the band rides up, change the band first (use sister sizing). If you’re spilling or gaping, adjust the cup (or the style).

Is it normal to be different sizes in different brands?
Yes—fabric stretch and cut vary. Use the calculator as a baseline and the fit check as the final answer.

Care Guide (so your bras keep their lift)

Most bras lose their support early because of heat and harsh washing. Gentle care makes a bigger difference than most people expect.

Final Thought

If you’ve been living in bras that dig, slip, ride up, or make you feel restricted, it’s not your body, it’s the fit.

Use the bra size calculator to get your starting point. Measure carefully. Then trust the fit check more than the label.

When the fit is right, you feel supported—and you stop thinking about your bra altogether.