First Bra Size Calculator UK
Teen & Junior Fitting Guide
Buying a first bra is a big milestone. This guide helps parents and teens find the right size using our free UK bra calculator — with a junior size chart, step-by-step measuring instructions, and tips for getting the perfect fit.
When Should You Get a First Bra?
There is no single “right” age for a first bra — every body develops at its own pace. Most girls in the UK start needing a bra or crop top between the ages of 9 and 14, but it can be earlier or later. Signs that it might be time include:
- 1Breast buds becoming visible under clothing
- 2Feeling self-conscious during PE or sports
- 3Wanting more support or coverage
- 4Needing a layer for comfort under school uniform
Types of First Bra
Crop Top / Bralette
Soft, unstructured, and wire-free. Perfect for early development (AAA–AA). Often the most comfortable first option.
Soft Cup Bra
Lightly padded or unpadded with no underwire. Gives gentle support and shape for AA–B cups. Great for everyday wear.
T-Shirt Bra
Smooth, moulded cups that sit invisibly under tops. Available from 28AA. Ideal for school uniforms and fitted clothing.
Sports Bra
Provides support during physical activity. Essential for PE and sports. Available in junior sizes from most UK retailers.
How to Measure for a First Bra
You will need a soft measuring tape. If you don't have one, wrap a piece of string around and then measure the string against a ruler. Measurements can be in centimetres or inches.
Measure Under the Bust
Wrap the tape snugly around the ribcage, just under the bust. Keep it level all the way around. This is the band measurement.
Measure Over the Bust
Measure around the fullest part of the bust. The tape should be level and not too tight — just resting gently. This is the bust measurement.
Calculate the Size
The band measurement gives you the band size (e.g. 28, 30, 32). The difference between bust and band determines the cup size. Use our free calculator below for instant results.
UK Junior Bra Size Chart
Most first bras fall within the 28AA to 34D range. Here is a quick reference chart for common junior/teen sizes available from UK retailers:
| Band Size | Under Bust (inches) | Cups Available |
|---|---|---|
| 28 | 27–29" | 28AA28A28B |
| 30 | 29–31" | 30AA30A30B30C |
| 32 | 31–33" | 32AA32A32B32C32D |
| 34 | 33–35" | 34A34B34C34D |
First Bra Fitting Tips
✅ Do: Start with Wire-Free
Wire-free bras are more comfortable for developing bodies. Save underwired styles until the bust is more fully developed.
✅ Do: Check the Band
The band should fit snugly but not dig in. You should be able to slide two fingers under the back band.
❌ Don't: Buy Too Big
It's tempting to buy a bigger size 'to grow into', but an oversized bra won't provide support and can affect posture.
✅ Do: Try Before Buying
Sizes vary between brands. Whenever possible, try on in-store. M&S, Next, and John Lewis all have teen ranges.
❌ Don't: Rely on Age
Bra size has nothing to do with age. A 10-year-old and a 14-year-old could easily need the same size.
✅ Do: Remeasure Regularly
Bodies change quickly during puberty. Remeasure every 3–6 months to ensure the bra still fits properly.
Where to Buy First Bras in the UK
Most UK high street retailers and online stores carry junior and teen bra ranges. Popular options include:
First Bra FAQ
What size is a first bra usually?+
Most first bras are between 28AA and 32B. The most common first bra size in the UK is a 30A or 28A, but every girl is different.
Should a first bra be padded?+
It's personal preference. A lightly padded bra can help with modesty under school uniform, but many teens prefer unpadded bralettes for comfort.
How do I know when I need a proper bra instead of a crop top?+
If a crop top no longer feels supportive enough — especially during exercise — or if you can see the outline through clothing, it might be time to try a cup-sized bra.
Can boys help with measuring?+
Measuring should be done by the person wearing the bra, or with a trusted female family member if help is needed. Privacy and comfort are important.
Ready to find the right first bra size?