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

Quick answer

Measure your band size by wrapping a soft tape snugly around your ribcage just under your bust, then measure your bust at the fullest point. Subtract the band from the bust to get your cup size. Re-measure every six months or after any weight change, because band size shifts more often than cup size.

A bra that fits should feel like a second skin, not a daily compromise. If you are constantly tugging at straps or spilling out of cups, the problem is usually the number, not the style. Learning how to measure bra size at home gives you a reliable starting point before you ever step into a fitting room or add a bralette to your cart.

This guide walks you through the two measurements you need, how to turn them into a size, and how to sanity-check the result against real-world fit. You will also see how stretch lace styles from Lace Laboratory behave differently from rigid bras, so you can choose the right size for the fabric you actually wear.

What you need before you start

You do not need a professional fitter or a special bra size calculator to get a solid baseline. A soft measuring tape, a mirror, and a non-padded bra or a fitted tank top are enough. If you do not have a soft tape, use a piece of string and measure it against a ruler afterward. The mirror helps you keep the tape level, which is the single biggest factor in getting an accurate number.

Wear the least padded bra you own, or go without if you are comfortable. A push-up bra adds inches that will throw off your bust measurement. Stand tall, relax your shoulders, and breathe normally. Do not pull the tape tight enough to compress your ribcage, and do not let it sag at the back. The tape should sit level all the way around, like a headband that is not digging in.

• Use a soft tape, not a metal carpenter's tape, so it follows your curves.
• Measure in front of a mirror to check the tape is level.
• Avoid measuring over thick clothing or a padded bra.

Step 1: Measure your band size

Wrap the tape around your ribcage, directly under your bust. The tape should sit snug against your skin but not leave red marks. Breathe out normally and check in the mirror that the tape is parallel to the floor at the front and back. Write down the number in inches. If it is an odd number, round down to the nearest even number for most sizing systems, because band sizes typically come in even increments.

For example, if your underbust measures 31 inches, your starting band size is usually 30. If it measures 32 inches, start with 32. Some brands run snug or loose, so treat this as a starting point rather than a final verdict. The band provides most of the support in a wired bra, so getting this number right matters more than the cup letter.

• Common mistake: pulling the tape too tight and compressing your ribcage.
• Checkpoint: the tape should stay level when you lower your arms.

Step 2: Measure your bust size

Wrap the tape around the fullest part of your bust, usually across the nipple line. Keep the tape level and snug but not tight. Do not pull it so close that it flattens your natural shape. Stand straight and look in the mirror to confirm the tape is not riding up at the back. Record this number in inches.

If you are between half inches, round to the nearest whole inch. For a more forgiving fit in stretch lace, you can also measure while wearing a non-padded bralette that you already own and like. That gives you a real-world reference point rather than a bare-skin number, which can be useful if you plan to buy soft cup styles.

• Common mistake: measuring over a padded or push-up bra.
• Checkpoint: the tape should touch your back at the same height as the front.

Step 3: Calculate your cup size

Subtract your band measurement from your bust measurement. The difference in inches corresponds to a cup letter: 1 inch is typically an A, 2 inches a B, 3 inches a C, 4 inches a D, 5 inches a DD or E, and so on. For example, a 34-inch band and a 37-inch bust gives a 3-inch difference, which points to a 34C. Write this down as your starting size.

This calculation is a guide, not a law. Different brands grade cups differently, and your shape, density, and ribcage flare all affect fit. If you are between cup sizes, choose the smaller cup for stretch lace styles that relax with wear, and the larger cup for rigid, structured bras. Always check the brand's specific size chart before ordering.

• Common mistake: assuming the difference always maps to the same cup across brands.
• Checkpoint: if the difference is less than 1 inch, you may be an AA or a band-only size.

Step 4: Test the sister size

If your calculated size feels slightly off, try a sister size. Sister sizes have the same cup volume but a different band length. To go down a band, go up a cup; to go up a band, go down a cup. For example, if 34C feels tight in the band but right in the cup, try 36B. If 34C feels loose in the band but the cup is perfect, try 32D.

Sister sizing is especially useful with stretch lace bralettes, which often have more give than wired bras. A bralette that stretches up to 150% may fit comfortably across two band sizes, so your sister size can be a valid alternative rather than a compromise. Keep both sizes in mind when you shop and check the product's size options.

• Common mistake: changing both band and cup in the same direction.
• Checkpoint: the sister size should feel similar in cup volume, not tighter or looser.

Step 5: Check the fit on your body

Put on a bra in your calculated size and check three things: the band should sit level and snug around your ribcage, the center front should lie flat against your sternum, and the cups should contain your breast tissue without gaps or spillage. Raise your arms and move around. If the band rides up at the back, it is too loose. If the wires dig into your ribs, the band is too tight or the cup is too small.

For wire-free styles like bralettes, the fit check is slightly different. The elastic band should stay in place without cutting in, and the cups should not gape when you bend forward. Stretch lace will relax slightly with wear, so a bralette that feels a touch snug at first is often the better choice. If it feels perfect on the loosest setting, it may stretch out too much over time.

• Common mistake: judging fit only while standing still.
• Checkpoint: the band should not leave deep red marks after 10 minutes.

Your at-home measuring steps at a glance

1. Gather your tools: Use a soft measuring tape, a mirror, and a non-padded bra or fitted tank. Checkpoint: the tape should be flexible and at least 60 inches long.
2. Measure your band: Wrap the tape snugly under your bust, keep it level, and round down to the nearest even number. Common mistake: pulling too tight and compressing your ribcage.
3. Measure your bust: Wrap the tape around the fullest part of your bust, keeping it level and snug but not tight. Checkpoint: the tape should not flatten your natural shape.
4. Calculate your cup: Subtract your band from your bust. Each inch of difference equals one cup letter. Common mistake: assuming every brand uses the same cup grading.
5. Try a sister size: If your size feels off, go down a band and up a cup, or up a band and down a cup. Checkpoint: the cup volume should stay the same, not change.
6. Do a real-world fit check: Wear the bra for 10 minutes, move around, and check the band, center front, and cups. If the band rides up, size down; if it digs in, size up.

How Lace Laboratory styles fit into your size

• Curvy Lace Bralette - Mint: Specially designed and sized for full busts, with power mesh lining for extra bust support and wide, adjustable straps. If your bust measurement is several inches larger than your band, this style is built to support without wires, so you can use your calculated size with confidence.
• Lace Bralette - Lemon Sorbet: Wire-free and non-padded, crafted in signature stretchable lace that stretches up to 150% for barely-there comfort and support. The high stretch means it accommodates small fluctuations in band size, making it a forgiving choice if you are between sizes.
• High Waist Brazilian - Forest Muse: High-waisted design supports you in all the right places for a smooth, figure-shaping silhouette, while the cheeky Brazilian back keeps things light and comfortable, crafted in signature stretch lace that stretches up to 150%. Once you know your band size, you can pair your bralette with a matching bottom in the same size for a set that fits consistently.

Measuring your bra size at home takes five minutes and saves you from guessing. Start with your band and bust numbers, calculate the cup, and test a sister size if you are between sizes. Then check the fit on your body, not just the label. With the right starting size, stretch lace styles like those from Lace Laboratory can feel made for you.