How to measure your bra size
Four measurements with a soft tape measure, in about five minutes. These are the same steps our calculator uses, so what you measure here is exactly what it asks for. You’ll take two measurements around your ribcage and two around your bust. Each one tells the calculator something different, so it’s worth taking them carefully and in order.
What you need
- A soft tape measure, the flexible kind used for sewing. A rigid DIY tape can’t follow the curve of your body. No tape? See what to do without one.
- A mirror, if you have one. It helps you check the tape is level across your back.
- No bra, or a thin unpadded one. Padding and thick fabric add to the measurement.
- Somewhere to note the numbers, and about five minutes.
Padding adds to your bust measurement and can make the result about one cup too large. If you did measure over padding, tell the calculator: it will warn you and lower its confidence score.
Step 1: Prepare
- Take off any padded or moulded bra. Measure without a bra, or over a thin, unpadded one.
- Stand upright in front of a mirror, with your shoulders relaxed and your arms by your sides.
- Check you are reading the tape from its zero end.
- Decide whether to read centimetres or inches. Either works, as long as you use the same unit for all four.
Step 2: Snug underbust
- Stand up straight and wrap the tape around your ribcage directly under your breasts, where a bra band sits.
- Keep the tape level all the way round. Checking in a mirror helps.
- Breathe out and pull the tape firm, as tight as is comfortable to hold for a moment.
This measurement sets your band, and the band gives a bra most of its support, so the tape should be firm. Firm means snug, not painful.
Step 3: Loose underbust
- Keep the tape in the same place under your breasts.
- Breathe normally and let the tape rest flat against your skin without pulling it in.
- This shows how much your ribcage and soft tissue compress, which helps choose between two bands.
This should be the same as your snug measurement or larger. If it comes out smaller, the two have probably been swapped, so take both again.
Step 4: Standing bust
- Stand upright with your arms relaxed by your sides.
- Wrap the tape around the fullest part of your bust, keeping it level across your back.
- Keep the tape loose enough that it does not press in.
Check the tape in the mirror before you read it. If it has dipped at the back or slipped at the front, level it and measure again.
Step 5: Leaning bust 90°
- Bend forward from the hips until your back is roughly level with the floor.
- Let your breasts hang forward naturally.
- Wrap the tape around the fullest part, keeping it loose. This captures tissue a standing measurement can miss.
Leaning is usually the same as your standing measurement or larger. If your standing figure is noticeably bigger, the tape has probably slipped, so try again. If bending forward is uncomfortable, lean only as far as is comfortable, or enter your standing measurement again if you can’t lean at all. The calculator uses whichever bust measurement is larger, although a partial lean may not pick up as much tissue as a full one.
Step 6: Enter your measurements
Enter all four numbers in the calculator and choose the unit you measured in. Then tell it what you were wearing: no bra, a thin unpadded bra, or a padded bra.
You’ll see your size using the modern method, with the traditional method alongside for comparison, your sister sizes, and a confidence score that explains how consistent your measurements are. If your result sits midway between two cups, both are shown. The calculation runs in your browser, so your measurements are never sent to us.
Tips for accurate measurements
- Measure twice. Take each measurement twice and use the average. If the two readings are far apart, check where the tape is sitting, take a third and average the two closest.
- Keep the tape level. A tape that rides up or dips at the back measures a different part of your body from the front. Check it in the mirror before you read the number.
- Check an old fabric tape. Fabric tapes can stretch with use. Lay yours against a ruler: if the markings no longer line up, use a different tape.
- Ask for help at the back. Someone you’re comfortable with can check the tape is level behind you, even if you hold and read it yourself.
- Don’t over-round. Reading to the nearest 0.5 cm or 0.25 inch is precise enough. Enter what the tape shows and let the calculator do the rounding.
- Measure in similar conditions each time if you’re comparing results over time, for example wearing the same thing. The size tracker keeps dated results on your device.
For the errors that most often lead to the wrong size, see our guide to common measuring mistakes.
Why four measurements?
Most charts use two numbers. The calculator asks for four because each answers a different question:
- Snug underbust sets your band.
- Loose underbust shows how much soft tissue compresses under the tape. When your snug measurement falls exactly between two bands, a large gap tips the result to the firmer band.
- Standing and leaning bust set your cup. Leaning forward picks up tissue that a standing measurement can miss, and the calculator uses whichever is larger.
Having four also lets the calculator check your measurements against each other. If something doesn’t add up, such as a loose underbust smaller than the snug one, it asks you to re-measure or lowers its confidence score rather than guessing. Our methodology page lists every check.
Centimetres or inches
The calculator has a unit switch for centimetres and inches. Choose whichever your tape shows most clearly. If you switch after typing, the numbers you’ve already entered are converted for you, rounded to the nearest 0.5 cm or 0.25 inch, so you don’t need to retype them.
The unit doesn’t change your result. Sizes are worked out in inches, because UK cup sizes step up one letter for each inch (2.54 cm) of difference between bust and band. If a number looks as though it was measured in the other unit, such as an underbust in centimetres typed while inches is selected, the calculator asks whether you meant the other unit instead of guessing.
No tape measure?
A length of string or ribbon that doesn’t stretch can stand in for a tape: wrap it around, mark where it meets with a pen, then measure the marked length against a ruler. Take each of the four measurements the same way.
If you can’t do that, our no-tape-measure tool estimates a size from a bra you already own or from your clothing size. It is a rougher starting point than measuring, so measure properly when you can.
Use the tools
Bra Size Converter
Four measurements, both band methods, sister sizes and a confidence score.
No Tape Measure
Get a rough bra size estimate from a bra you already own or your dress size.
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