How to Measure Bra Size at Home: A Step-by-Step Guide

Quick answer

Measure your band size snugly around your ribcage just under the bust, then measure your bust at the fullest point. Subtract the band measurement from the bust measurement to find your cup size. Re-measure every six months or after any weight change, because bra sizing shifts more often than most people expect.

Most fitting problems start with a tape measure that was never used, or was used once and never repeated. If your straps dig in, your band rides up, or the wires sit on breast tissue instead of around it, the size is usually the culprit, not the bra.

This guide walks through bra fitting at home in five ordered steps, with the mistakes that throw each measurement off. You only need a soft tape measure, a mirror, and a few minutes in a well-lit room.

Before you start: what you need and what to wear

Use a soft, flexible tape measure rather than a rigid ruler, and stand in front of a mirror so you can check that the tape stays level all the way around. Wear an unpadded or lightly padded bra, or no bra at all if you prefer. A heavily padded or push-up style adds volume that is not yours, which inflates the bust measurement.

Keep the tape snug but not tight. You should be able to slide one finger under it. If the tape leaves a red mark or you have to tug to close it, you are pulling too hard, and the resulting number will be too small.

• A soft tape measure and a mirror are enough; no special tools required.
• Avoid measuring over thick clothing, padded cups, or a sports bra that compresses the bust.

Step 1: Measure your band size

Wrap the tape around your ribcage, directly under your bust, keeping it parallel to the floor. Breathe out normally and record the number in inches. This is your underbust measurement, and it is the starting point for your band size.

The most common mistake here is letting the tape dip at the back. If the back of the tape sits lower than the front, the measurement reads larger than it is. Check the mirror and adjust until the tape is level.

• Round to the nearest whole inch before converting to a band size.
• If the number is even, add four inches; if odd, add five. That total is your band size.

Step 2: Measure your bust size

Wrap the tape around the fullest part of your bust, usually across the nipple line, and keep it level. Stand straight with your arms relaxed at your sides rather than lifting them, which can change the reading. Record the number in inches.

Do not pull the tape tight across the bust. The tape should rest against the tissue without compressing it. If you are between two numbers, note both and use the larger one for the cup calculation, then adjust based on how the bra feels.

• Keep arms down; raising them can shift the tape and shrink the reading.
• Write down the number immediately rather than trying to remember it.

Step 3: Calculate your cup size

Subtract your band size from your bust measurement. The difference in inches determines your cup letter: one inch is an A, two inches is a B, three inches is a C, four inches is a D, and so on. This is the core of any bra size calculator guide, and it is simple arithmetic once you have both numbers.

A common error is using the underbust measurement instead of the final band size in the subtraction. Use the band size you calculated in Step 1, not the raw underbust number, or the cup will come out one size too large.

• Difference of 1 inch = A, 2 = B, 3 = C, 4 = D, 5 = DD.
• If the difference falls between two cup sizes, try the smaller cup first and size up only if it cuts into breast tissue.

Step 4: Read a bra size chart correctly

A bra size chart explained properly is a conversion tool, not a rulebook. Band sizes and cup letters vary slightly between brands, and the same 34C can fit differently across styles. Use the chart to find your starting size, then treat the first try-on as a check rather than a verdict.

Pay attention to whether the chart uses inches or centimetres, and whether it lists band size or underbust measurement. Mixing those up is one of the most frequent reasons people order the wrong size online.

• Check the unit of measurement before matching your numbers to the chart.
• Note the brand's guidance on sister sizes, which let you adjust band and cup together.

Step 5: Test the fit and adjust

Put the bra on and fasten it on the loosest hook. The band should sit level and firm around your ribcage without riding up when you raise your arms. The centre front should lie flat against your sternum, and the cups should contain all breast tissue without gaps or spillage.

If the band rides up, go down a band size and up a cup size. If the cups gape, go down a cup size. If the wires dig into your sides, the cup is too small. Adjust one variable at a time so you can tell what actually changed.

• Fasten on the loosest hook so the bra can be tightened as the elastic relaxes over time.
• Scoop breast tissue forward and up into the cups before judging the fit.

Your five-step measuring routine

1. Measure underbust for band size: Wrap the tape snugly under your bust, keep it level, and record the number in inches. Add four if even, five if odd. Checkpoint: the tape should not dip at the back.
2. Measure bust at the fullest point: Keep the tape level across the nipple line with arms down, and record the number without compressing the tissue. Checkpoint: you should still be able to slide one finger under the tape.
3. Subtract band from bust for cup size: Use the band size from Step 1, not the raw underbust number. One inch equals an A, two a B, three a C, and so on. Checkpoint: if the result is between cups, start with the smaller one.
4. Match your numbers to the brand's size chart: Confirm whether the chart uses inches or centimetres and whether it lists band size or underbust measurement before choosing. Checkpoint: treat the chart as a starting point, not a final answer.
5. Try on, then adjust one variable at a time: Fasten on the loosest hook, scoop tissue into the cups, and check whether the band stays level and the centre front lies flat. Next step: if the band rides up, go down a band size and up a cup size.

Bras that make fit easier to judge

• Favorlace Triangle bra remov. pads | 087512-08S412: The bra pads are removable, and the straps and back are adjustable. Removable pads let you see how the cup fits without added volume, and adjustable straps and back make it easier to fine-tune the band and shoulder tension after measuring.
• CottonLace Multipack Girls padded triangle bra | 030100-08S338: Padded cups create a natural silhouette, whilst the wire-free design ensures a particularly comfortable fit, with adjustable straps and a hook-and-eye fastening. A wire-free style with adjustable straps is a forgiving choice when you are between sizes or still confirming your measurement, because it applies less pressure at the underband.
• Cotton Ornaments Padded triangle bra | 080931-08S482: Sartorial lace detailing elevates this wireless bra, while a soft lining ensures your comfort. A soft lining and wireless construction reduce the chance of irritation if your first measured size turns out to be slightly off and you need to exchange it.

Measuring at home takes five minutes and removes most of the guesswork from buying bras online. Write your numbers down, re-check them every six months, and adjust one size variable at a time until the band stays level and the cups sit flat. That routine will serve you better than any single size label.