How to Measure Bra Size
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Learning how to measure bra size takes two minutes and one soft tape. You will take exactly two measurements — the underbust around your ribcage and the bust around the fullest part — then let the calculator convert them into a starting size. No shop, no fitter, no guessing.
This guide shows how to measure bra size correctly in both inches and centimetres, which mistakes silently ruin the numbers, and what to do once you have them. Follow the animation on the right as you go.
Quick answer
To measure bra size, wrap a soft tape snugly around your ribcage directly under the bust — that is the underbust. Then wrap it loosely around the fullest part of the bust, keeping it level. Enter both numbers into a bra size calculator to get your starting size; the underbust sets the band and the difference between bust and underbust sets the cup.
6
sizing systems (US, UK, EU, FR/ES, AU/NZ, JP)
460+
charted sizes with bust ranges
2
measurements needed (underbust + bust)
What you need to measure bra size
Before you learn how to measure bra size, collect the right tools. The list is short, and every item matters: a distorted tape or a padded bra will move your answer by a full cup letter.
- A soft measuring tape (cloth or fibreglass) — not a stiff metal tape.
- An unpadded bra or a thin fitted top; padding adds centimetres you do not have.
- A mirror to keep the tape level — the single most common error is a tilted tape.
- Relaxed posture: shoulders down, breathing normally, arms at your sides.
- A notebook, because how to measure bra size ends with two numbers worth keeping.
- Thirty calm seconds — how to measure bra size rewards an unhurried posture.
Step 1 — Measure your underbust
The underbust is the foundation of every bra size, so this is where how to measure bra size begins. Wrap the tape around your ribcage, directly under the root of your bust, where the band of a well-fitted bra would sit. The tape should be snug — firm enough that it cannot slide, loose enough that you can slide one finger underneath.
Keep the tape parallel to the floor all the way around; check the mirror. Breathe normally — a deep inhalation can add two centimetres, and holding your breath can subtract them. Round to the nearest half inch or half centimetre and write the number down. If the tape lands on an odd number of inches, keep it as-is: the calculator does the band rounding for each system itself.
Step 2 — Measure your bust
Now measure the bust: wrap the tape around the fullest part of your breasts, usually across the nipples, without compressing the tissue. The tape should rest lightly on the bust — if it presses in, the cup result will run small; if it hangs loose in the back, it will run large.
Wear an unpadded bra or a thin top so the tape follows the body, and keep it level front and back. Many people find their bust is slightly fuller on one side — always measure the fuller side or measure both and use the larger number. This is also exactly how to measure bust for any clothing purpose, not only bras.
Step 3 — Turn the numbers into a starting size
This is where the guide meets arithmetic. Enter the underbust and bust into the calculator below and it will resolve the band from the underbust, the cup from the difference between bust and underbust, and show the result in six systems. For example, an underbust of 32 inches with a bust of 37 inches gives US 32DD, UK 32DD, EU 70E, FR/ES 85E, AU/NZ 10DD and JP E70.
Want the full theory first? The bra sizes guide explains what the number and the letter each mean, and the cup bra measurement page focuses on how the cup half is derived from your two tape readings.
Common mistakes when measuring bra size
Most wrong sizes come from five recurring errors. Scan this list before you trust your numbers:
- A tilted tape — riding up at the back under-reports both measurements.
- Measuring over bulky or padded clothing, which inflates the bust.
- Pulling the underbust tape too tight, which inflates the cup letter.
- Compressing the bust tape, which deflates it.
- Mixing centimetres and inches between the two measurements — always one unit for both.
- Skipping the mirror check — how to measure bra size depends on a level tape.
- Rounding too early — subtraction is part of how to measure bra size, so round last.
Why technique beats formulas
People ask how to measure bra size expecting a formula, but the formula is the easy part; the tape placement is the skill. A one-inch error in the underbust moves the band a full size. A one-inch error at the bust moves the cup a full letter. Re-measure twice on different days if your first attempt feels off — consistent numbers across days are the strongest signal you measured correctly. That repeatability is the real proof of how to measure bra size done well.
Once the measurements are right, respect the result as a starting point, not a verdict. Check the fit itself with our bra fit guide: level band, anchored gore, cups that neither spill nor gape, straps that carry almost no weight.
When to re-measure
Revisit how to measure bra size every six to twelve months, and immediately after weight change, pregnancy, breastfeeding, or any hormonal treatment. Band elasticity also fades — a bra that fit when new may sit looser after a year of wear, which is a bra problem, not a body problem. Refreshing how to measure bra size is the cheapest wardrobe maintenance there is.
How to measure bra size: a recap you can memorise
Strip the process to one sentence: snug tape under the bust, loose tape across the fullest part, both level, then subtract — that is how to measure bra size. The underbust becomes the band; the difference becomes the cup; the calculator turns both into six labels. Everything else in this guide — posture, clothing, mirror checks — exists to protect those two numbers from error.
People who learn how to measure bra size once tend to keep the skill for life, because the technique transfers to every brand and every country. Re-measure after any body change, revisit this page whenever the numbers feel stale, and remember the golden rule of how to measure bra size: two honest readings beat ten hopeful guesses. Knowing how to measure bra size also protects you from vanity sizing, because your own numbers — not a brand flattering label — become the reference for every size chart you read. That is the quiet superpower of learning how to measure bra size: the skill works in every store, in every country, for every brand, forever.
How to measure bra size — the checklist version
Some readers want the tutorial; some want the checklist. Here is how to measure bra size in six tickable lines — pin it, screenshot it, or read it once before every measuring session.
- Grab a soft tape — the only tool how to measure bra size truly requires.
- Underbust: snug, level, directly under the root — where how to measure bra size begins.
- Bust: loose, level, across the fullest part — the second half of how to measure bra size.
- Subtract: the bust minus underbust difference completes how to measure bra size.
- Convert: feed both numbers to the calculator and how to measure bra size becomes six labels.
- Verify: fit checks confirm what how to measure bra size proposed.
- Repeat: run how to measure bra size twice, a day apart, to confirm.
- Record: log the pair, because how to measure bra size is only as good as its inputs.
Frequently asked questions
How do you measure bra size at home?
Measure the underbust snugly around the ribcage directly under the bust, then the bust loosely around the fullest part, keeping the tape level. Enter both numbers into the calculator on this page to get your starting size in six systems. That is how to measure bra size end to end in two minutes.
Do I measure bra size with a bra on or off?
An unpadded bra or a thin fitted top gives the most consistent result. Avoid padded, moulded or push-up styles — they add volume that the tape will read as yours. Fabric choice is part of how to measure bra size correctly.
How to measure bra size in cm vs inches?
The technique is identical; only the unit changes. Use one unit for both measurements. US, UK and AU/NZ labels come from inches, while EU, FR/ES and JP labels are centimetre-based — the calculator converts internally so you never have to. Unit choice never changes how to measure bra size itself.
How do I check bra size without measuring?
Check the fit of your current best bra: a band that rides up is loose, cups that gape are large, a gore that floats means the cup is small. Our fit guide maps each symptom to likely causes. But for a number, you need the two measurements — there is no shortcut that is also honest. Fit signs supplement how to measure bra size; they never replace it.
How tight should the underbust tape be?
Snug but not compressing: you should be able to slide one finger under the tape, and it should stay put when you move. The band of the final bra should feel the same way on the middle hook. That same finger test appears in every how to measure bra size tutorial.
Why does my size differ between brands?
Brands cut patterns independently of the size chart arithmetic. Keep your measurements, not your old label, as the source of truth and re-run the calculator per brand market when needed. Your technique for how to measure bra size stays constant across brands.
How to measure bra size without a tape?
Use a piece of string or a phone charging cable marked against a ruler — the technique for how to measure bra size matters more than the tool. Mark the underbust and bust lengths, measure both against the ruler, and enter them into the calculator.
How to measure bra size for the first time?
Follow the animation above: underbust tape snug under the root, bust tape level at the fullest point, then enter both numbers into the calculator. Learning how to measure bra size takes about two minutes and repeats in thirty seconds, which is why how to measure bra size is the first skill every fitting guide teaches.
Should I learn how to measure bra size in cm or inches?
Either — pick one unit for both readings. If you are shopping continental brands, centimetres feel natural; for US and UK labels, inches. The calculator converts internally, so how to measure bra size never depends on the unit you choose.
Is it easier to learn how to measure bra size in cm or inches?
Neither — how to measure bra size is a technique, not a unit. Pick the unit you will shop in, keep it consistent for both readings, and let how to measure bra size do the rest through the converter. Consistency, not the unit, is what makes how to measure bra size reliable.
How to measure bra size in under a minute?
Underbust, bust, subtract, convert — how to measure bra size is those four moves once the technique is familiar. Run it with the calculator and the minute includes the result.
Does how to measure bra size differ for sports bras?
The measurements are identical; only the brand chart changes. Learn how to measure bra size once and apply it to every bra category.
Sources & standards
Every size on this site is cross-checked against these published standards and chart families before it ships.
- 2017
ISO 8559-1:2017 — Size designation of clothes — Part 1: Anthropometric definitions for body measurement
Defines the body measurement points (chest/bust girth, underbust girth) this site measures.
- 2017
EN 13402 (label family) — Size designation of clothes — European size labelling
Basis of the continental EU band ladder (65, 70, 75 …) in 5 cm steps.
- 2023
JIS L 4006:2023 — Sizing systems for foundation garments
Japanese foundation-garment sizing; the label family behind JP cup-first sizes such as C75.
- 2019
KS K 9404 — Sizing systems for foundation garments (Korea)
Korean foundation-garment sizing; referenced while the KR system awaits full verification.
- 2025
Multi-source retail consensus — US, UK, FR/ES and AU/NZ bra size charts (cross-brand average)
Inch-based band rounding, UK double-letter cup ladder, FR/ES +15 offset and AU/NZ dress-size bands.
By Bra Size Calculator ·