How do you measure your bra size?
Two measurements with a soft tape measure tell you your bra size: your band (under the bust at the ribcage) and your bust (across the fullest point of the chest). Subtract band from bust — each inch of difference equals one cup letter (1″=A, 2″=B, 3″=C, 4″=D, 5″=DD). Combine the band number, rounded to the nearest even inch, with the cup letter to get your size. The whole process takes about five minutes with a soft tape, and the math is identical whether you measure in inches or centimeters.
Most bra wearers are in the wrong size — and most have been for years. Research consistently puts the figure at 70–85%, with roughly 70% wearing a size that's too small and another 10% wearing one that's too large. The average US bra size sits around 34DD, but the average is statistical context, not a target — what matters is the math your own measurements produce. The fix isn't complicated. This guide covers the home method that gets you the right answer, what to do when measurements land between sizes, how to use sister sizing to fine-tune, and why the +4-inch method (still taught by some retailers) produces the bands that ride up your back.
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Shop All Bras → Use the Calculator →- Two measurements: band (under the bust) and bust (across the fullest point).
- Subtract band from bust. Each inch of difference equals one cup letter.
- 1″ = A, 2″ = B, 3″ = C, 4″ = D, 5″ = DD, 6″ = DDD/F, 7″ = G.
- Round your band to the nearest even inch — bra bands sell in even sizes only.
- Measure the band without a bra; measure the bust in an unlined, non-padded bra.
- Do not add 4 inches — the +4 method is outdated and produces too-loose bands.
- If your numbers land between sizes, sister sizing gives you three equivalent options.
What You'll Need
Before you start, gather four things. None are specialized — they live in most homes already.
Cloth or vinyl, the kind used in sewing — not a metal carpenter's tape. If you don't have one, a non-stretchy string or ribbon plus a ruler works as a substitute.
Wear an unlined, non-padded bra you already trust for the bust measurement. Padding adds projection and will inflate your number by half a cup or more.
Helpful for keeping the tape level all the way around your back. A second pair of hands works too if you have someone available.
You'll subtract one number from another. Phone calculator is fine. Write down your band and bust measurements before doing the math so you don't lose track.
Step 1 — Measure Your Band Size
Your band size is the circumference of your ribcage directly under your bust, measured in inches. The band carries roughly 80 percent of a bra's support — getting this number right matters more than getting the cup right.
Measure the Underbust Snugly and Level
Without a bra, wrap the tape measure around your torso directly under the bust — at the inframammary fold, the crease where the breast meets the ribcage. Pull the tape snug, but not constricting. The tape should sit parallel to the floor all the way around your back.
- Round to the nearest even inch. Bra bands come in even sizes (28, 30, 32, 34, 36, 38). If you measure 33, round to 32 or 34.
- When in doubt, round down. Bands stretch with wear; a firmer starting band lasts longer. If 32 cuts into your skin or restricts breathing, sister-up to 34.
- Don't add inches. Older fitting methods told you to add 2, 4, or 5 inches to your underbust measurement. That dates from a time when elastic was less stretchy and is now the leading cause of mis-fit.
If you were taught to add four inches to your underbust to find your band size, ignore it. Modern band elastic is engineered to fit your direct measurement. Adding inches gives you a band that rides up the back, transfers all support to the straps, and stops working within months. We compare both methods side-by-side later in the article.
Step 2 — Measure Your Bust Size
Your bust measurement is the circumference around the fullest part of your chest. Combined with the band, it tells you how much volume your cups need to hold.
Measure Across the Fullest Point
Put on an unlined, non-padded bra that already fits well. Wrap the tape around the fullest part of your bust — usually across the nipple line, but the exact location varies by body. Keep the tape parallel to the floor, snug but not compressing the tissue.
- Don't compress. The tape should rest on the breast, not flatten it. Compression underestimates volume.
- Lean forward 90° if you're full-busted. For C cup and above, lean over so your bust falls naturally and measure in that position. Standing upright can underestimate by an inch or more — about a full cup size.
- Take a couple of readings. Stand up, lean forward, take both. If they're more than half an inch apart, use the larger number.
Step 3 — Calculate Your Cup Size
Subtract your band measurement from your bust measurement. The difference, in inches, maps directly to a cup letter. Each inch of difference is one cup size.
Combine your band and cup to get your size. If your band measures 33 inches (rounded down to 32) and your bust measures 36 inches, the difference is 4 — your size is 32D. If your band is 36 and your bust is 39, you're a 36C.
Or Skip the Math — Use the Calculator
The arithmetic is straightforward, but if you'd rather skip it: enter your two measurements below and the calculator returns your size in US, UK, EU, French, Australian, and Japanese sizing — plus your sister sizes. Switch units between inches and centimeters as needed. For a full international reference table, see our bra size conversion chart.
Find Your Size Across Six Countries
Enter your underbust and full bust below. The calculator returns your size in US, UK, EU, French, Australian, and Japanese sizing — plus your sister sizes. Switch units between inches and centimeters as needed.
What to Do When Your Measurement Lands Between Sizes
Bras come in discrete sizes, but bodies don't. You'll often measure half an inch off, or find the band fits but the cup feels off, or vice versa. Sister sizing solves most of this.
Sister sizes are pairs that share the same cup volume but ride on a different band. The math: go up one band, down one cup letter (sister-up). Go down one band, up one cup letter (sister-down). For a 34C, the sister sizes are 32D and 36B — all three hold equivalent cup volume on different bands.
Two Common Patterns and the Fix for Each
Cup feels right but the band rides up the back? The band is too loose — sister-down. A 34C wearer with this issue often fits a 32D better.
Band feels right but cups gape or spill? Adjust the cup at the same band first. If you can't get a clean fit at any cup letter, the brand's pattern may not match your shape — try a different cut or brand.
Both feel half-off? Try the size both up and down a band, plus the cup adjustment. Most wearers fit one of three or four equivalent sizes — finding which one your body prefers takes a couple of try-ons. (See the full guide to sister sizes for more.)
Why the +4 Method Gives You the Wrong Size
If you've ever been measured at a department store and walked out wearing a 36B when you suspected you were closer to a 32D, you were probably fit using the +4 method — adding 4 inches to your underbust to determine the band size. The method dates from the 1950s, when bra elastic was significantly less stretchy than modern materials. It hasn't been updated. It is now the single biggest cause of bra mis-fit, including most of the 80% wrong-size statistic.
Here's what happens at common underbust measurements:
| Underbust | +4 Method (outdated) | Direct Measurement (correct) | Difference |
|---|---|---|---|
| 28″ | 32 band | 28 band | 4 sizes too loose |
| 30″ | 34 band | 30 band | 4 sizes too loose |
| 31″ | 36 band (rounded up) | 32 band (rounded up) | 2 sizes off |
| 32″ | 36 band | 32 band | 2 sizes too loose |
| 34″ | 38 band | 34 band | 2 sizes too loose |
| 36″ | 40 band | 36 band | 2 sizes too loose |
| 38″ | 42 band | 38 band | 2 sizes too loose |
The result of a too-loose band: it rides up the back, transfers all weight to the straps (which then dig into your shoulders), and stretches out within weeks. To compensate, fitters trained on the +4 method historically added a smaller cup letter to maintain proportion — which is how a 32D wearer ends up in a 36B. Both numbers are wrong. The 32D fits.
A too-loose band cannot anchor the bra against the body, which means breast tissue is supported almost entirely by the shoulder straps. Research has linked chronically poor bra fit to upper back, neck, and shoulder pain — particularly for D cups and above where the unsupported weight is significant. The right band size isn't a vanity issue; it's a structural one.
Common Measurement Mistakes
Most home measurement errors fall into the same six categories. If your measured size feels wildly off from what you expect, scan this list before you trust the number.
Padding adds projection that the tape reads as breast volume. Use a non-padded, unlined bra — or a thin t-shirt over bare skin if a fitted bra isn't available.
If the tape arcs upward at the back, the band reads tighter than reality. Use a mirror to confirm the tape sits parallel to the floor on both sides.
A relaxed underbust tape over-reads by an inch or more. The band should be snug and firm — pulled gently against the ribcage, not draped on top.
For C cup and above, standing upright lets tissue rise toward the chest wall and under-reads the bust. Lean forward to 90° so the bust falls naturally before measuring.
A size you were measured into five years ago may not fit today. Bodies change with weight, hormonal shifts, and time. Re-measure every six to twelve months.
The +4 method (or +2, or +5) is outdated. Use your direct underbust measurement rounded to the nearest even inch. Adding inches creates a too-loose band — the most common mis-fit pattern.
How to Tell If Your Current Bra Doesn't Fit (and What to Try Instead)
Your measured size is the starting point — fit confirms it. Use this table to diagnose what your current bra is doing wrong, what it means, and which adjustment to try. Most issues map to band, cup, or strap; most fixes are sister-size adjustments.
| Symptom | What It Usually Means | What to Try Next |
|---|---|---|
| Band rides up the back | Band is too loose — the most common mis-fit | Sister-down (e.g., 36C → 34D) |
| Cup gapes at the top | Cup is too large, or band is too loose pulling cup away from chest | Same band, smaller cup; or sister-down if band is also loose |
| Spillage over the top of the cup | Cup is too small for breast volume | Same band, larger cup; or sister-up if band is also tight |
| Underwire pokes at the side | Cup is too small for the breast root, pushing the wire outward | Larger cup at same band |
| Center bridge floats off the chest | Cup is too small, or wires too narrow for chest width | Larger cup first; if it still floats, try a different brand cut |
| Underwire sits on breast tissue | Wires too narrow for the breast root | Different brand cut with wider-set wires |
| Straps dig into shoulders | Band too loose — straps carrying weight that band should | Tighten band by one hook, or sister-down |
| Band is comfortable; bra still feels off | Brand pattern doesn't match your shape | Try a different brand or cup cut (full-coverage, balconette, plunge) |
When to Re-Measure
Bra size isn't a fixed number you set once and never revisit. Bodies change continuously, and cup volume in particular can shift more than people expect. Re-measure on a schedule, and re-measure whenever any of these triggers fire:
- Every 6–12 months as a baseline, even without obvious changes.
- Weight changes of 10 lb or more — both directions. Cup size often shifts before the scale shows much movement.
- Hormonal birth control changes — measure 3 months after starting or switching.
- Pregnancy — re-measure each trimester. Bust and band can both grow significantly.
- Postpartum and breastfeeding — multiple times. Size often fluctuates daily during early breastfeeding.
- Menopause and HRT changes — hormonal shifts can change cup size by a full letter or more.
- Major training/exercise changes — adding or removing weight training, particularly chest exercises.
- Post-surgery recovery — particularly chest, shoulder, or abdominal procedures.
- If a familiar bra suddenly feels wrong — your body has changed, even if you can't see it.
"Bra fitting feels mysterious until you understand it as arithmetic. Two measurements, one subtraction, an even-number rounding rule. The rest is brand variation — which is real, but it's a much smaller effect than getting the math right in the first place."
— HauteFlair Fit Editorial Team
Frequently Asked Questions About Measuring
How do I measure my bra size at home?
What is the right way to measure my band?
What is the right way to measure my bust?
Should I round up or down if my band is between sizes?
How often should I re-measure?
Can I measure without a tape measure?
What if my bust measurement is smaller than my band?
Why is my measured size different from what I usually wear?
Should I measure with or without a bra?
Is the +4 method (adding 4 inches to band) accurate?
What is the average US bra size?
Does my bra size change during my period?
Why does my bust measurement change throughout the day?
Can men or non-binary people use this method?
Does this method work for sports bras?
This article is for informational and educational purposes. HauteFlair is not responsible for individual fit outcomes — bra sizing varies between brands and styles, and home measurements are a starting point rather than a guarantee. For best results, refer to each brand's specific size chart and consider a professional fitting consultation. For the full international size conversion reference, see the bra size conversion chart. Last reviewed: May 12, 2026.
