How to Measure Your Bra Band Size Correctly

Quick answer

Wrap a soft tape measure snugly around your ribcage, directly under your bust, keeping it level all the way around. Breathe out normally and read the number in centimetres or inches. That underbust measurement is your starting band size; if it lands on an odd number or between sizes, round to the nearest even band and let the cup size do the fine-tuning.

Most bra problems that feel like cup problems are actually band problems. A band that rides up, straps that dig in, or a centre that floats away from your chest usually trace back to a band measurement taken too loosely, too high, or over the top of a padded bra.

This guide walks through the bra fitting steps in order, from preparing the tape to checking the result against a bra you already own. You will also see why band size and cup size have to be read together, and how a small change in band changes the cup letter you need.

Before you measure: what to wear and what to skip

Measure on bare skin or over a thin, unpadded bra. A moulded or push-up bra adds bulk that inflates the underbust number, and a thick jumper or hoodie does the same. Stand in front of a mirror so you can see whether the tape is level at the back, and keep your arms down once the tape is in place.

Use a soft tailor's tape rather than a stiff builder's tape, and check it has not stretched by holding it against a ruler. If you only have a rigid tape, use a piece of string or a ribbon, mark the overlap, then lay it flat against a ruler. Write the number down rather than trying to remember it.

• Measure at the end of the day, not first thing in the morning, when your ribcage is at its natural size.
• Take the measurement twice. If the two numbers differ by more than 2 cm, re-check the tape level before trusting either one.

How to measure underbust without the tape drifting

Place the tape directly under your bust, where the underwire of a well-fitting bra would sit, not across the fullest part of your chest. Pull the ends together at the front and check in the mirror that the tape runs straight across your back rather than angling up towards your shoulder blades. An angled tape is the single most common reason a bra band measurement comes out too large.

Snug, not tight, is the target. You should be able to slide one finger under the tape, and you should be able to take a normal breath without the tape biting in. Exhale fully and read the number where the tape meets itself. If you are between two whole numbers, note both.

• Keep the tape parallel to the floor; if it dips at the back, the reading will be too small.
• Do not pull your shoulders back or hold your breath. Both change the ribcage shape and skew the result.

Turning the number into a band size

Band sizes are usually sold in even numbers, so round your underbust measurement to the nearest even number. If your measurement is already even, that is your band size. If it falls exactly halfway between two even numbers, try the smaller band first, because bands stretch with wear and a band that starts too loose will only get looser.

This rounding step is where band size vs cup size gets misunderstood. Moving down a band size means the cup volume gets smaller too, so you usually need to go up a cup letter to keep the same fit. A 34C and a 32D hold roughly the same volume, which is why a band change is never a band-only change.

• If your underbust measures 79 cm, round to 80 cm and start with the equivalent even band.
• If the band you try feels tight on the loosest hook, go up a band and down a cup rather than forcing the smaller band.

Check the result against a bra you already own

Before you buy anything, test the number on a bra in your drawer. Fasten it on the loosest hook and see where the band sits. A correct band sits level all the way around and stays put when you lift your arms. If the back rises, the band is too big; if the band digs in and leaves red marks that last, it is too small or the cups are too shallow.

This check also tells you whether your usual size is doing its job. Many people wear a band two sizes too large and compensate with a cup that is too small, which is why the straps end up carrying the weight. Once the band is right, the straps only need light tension to stay in place.

• Try the bra on the loosest hook first; you should still have tighter hooks available as the band relaxes.
• If the centre front does not sit flat against your chest, re-check the cup size before blaming the band.

Your bra band measurement in seven steps

1. 1. Strip back to bare skin or a thin bra: Remove padded or moulded bras, thick tops, and anything with a bulky seam across the ribcage, then stand in front of a mirror. Mistake to avoid: measuring over a padded bra, which adds centimetres that are not you.
2. 2. Find the underbust line: Locate the crease directly under your bust where a well-fitting underwire would sit. This is the line you measure, not the fullest part of your chest. Checkpoint: the tape should be below the bust tissue, not across it.
3. 3. Wrap the tape level and snug: Bring the tape around your back at the same height as the front, pull it snug, and confirm in the mirror that it is parallel to the floor. Mistake to avoid: letting the tape ride up at the back, which shrinks the reading.
4. 4. Breathe out and read the number: Exhale normally, keep your arms relaxed, and read the measurement where the tape meets. Repeat once to confirm. Checkpoint: two readings within 2 cm of each other are reliable; wider gaps mean the tape moved.
5. 5. Round to an even band size: Round your underbust measurement to the nearest even number. If it sits exactly between two, start with the smaller band. Mistake to avoid: rounding up out of habit, which gives you a band that starts loose.
6. 6. Adjust the cup when the band changes: If you move down a band size, go up a cup letter to keep the same volume. Band size vs cup size is a trade, not two separate numbers. Checkpoint: if the cups suddenly gape after a band change, the cup letter needs to go up.
7. 7. Test it on a real bra: Fasten a bra on the loosest hook and check the band sits level and stays put when you raise your arms. Next step: if the band rises, size down; if it digs in, size up or re-check the cup.

Bras that put the band measurement to work

• Peony Lace Full Cup Bra - Savvy Red: A full cup bra in Savvy Red with delicate lace, available in back sizes and cup sizes. A full cup shape covers more of the bust, so it is a useful style to test your measured band in if you prefer fuller coverage.
• Geo Lace Premium Support Bra - Burnt Orange: Features structured cups, a supportive underwire, and wide wings and straps that distribute weight for a secure fit. Wide wings and straps spread pressure across the ribcage, which matters most when you have just moved into a firmer band size.
• Willow Lace Midi Brief - Teal Blue: A low rise midi brief with lace panels in the front, full bottom coverage, and a cotton gusset, available in sizes. Once the band is sorted, a midi brief sits below the band line, so it will not compete with a snugly fitted bra.

A correct bra band measurement takes two minutes and saves you from years of straps doing work the band should be doing. Measure underbust, round to an even band, adjust the cup letter when the band changes, then confirm the result on a bra you already own before you buy.