Bra sizing tool
Sister Size Calculator
Use this tool when your cups feel close but the band feels wrong. It shows the nearest sister sizes, explains which direction to try first, and helps you avoid using sister sizing for problems it cannot really fix.
Best for
When your current cups feel mostly okay but the band feels too tight or too loose.
Fast rule
Band up = cup down. Band down = cup up.
Important note
If cups gape, spill, or wires hurt too, you may need more than a sister size.
Find Your Sister Size
Enter your current bra size, choose what feels wrong, and compare the safest nearby sister sizes without losing the core cup volume logic.
What sister sizing really does
Sister sizing keeps similar cup volume while changing the band fit.
That is why a sister size can help when your current bra size feels close in the cups but wrong in the band. It is useful for tight-band bras, loose-band bras, out-of-stock sizes, and brand differences, but it is not the right fix for every bra fit problem.
Band feels too tight, cups mostly okay
Try the looser-band sister size: go up one band size and down one cup letter.
Band rides up or feels too loose, cups mostly okay
Try the tighter-band sister size: go down one band size and up one cup letter.
Exact size is unavailable
A nearby sister size can be a practical fallback when your usual bra size is out of stock.
You are comparing brands
Sister sizing helps when one brand runs tighter or looser than another even in the same labeled size.
Band too tight? Go up one band size and down one cup letter.
Band too loose? Go down one band size and up one cup letter.
Example: if 34C feels too tight in the band, try 36B. If 34C rides up and feels loose, try 32D.
How to use the result
Use the sister size suggestion as a smart next size to try, not as a random shortcut.
The safest way to use a sister size calculator is to stay close to your likely base size, move one step first, and judge the new bra by real band support, cup fit, comfort, and overall stability.
Go one band up, one cup down
Use this when the band feels too tight but the cups feel reasonably close. Example: 34C → 36B.
Go one band down, one cup up
Use this when the band feels loose or rides up but the cups feel reasonably close. Example: 34C → 32D.
Stay close to one step first
One sister-size step is usually the safest move. Going too far can distort the fit even if the cup volume looks related on paper.
Do not use sister sizing for everything
If the bra also gaps, spills, pokes, or feels wrong in shape, the issue may not be solved by another nearby size.
Tight band sister size help
If your current bra feels tight around the ribcage but the cups are mostly fine, try the next looser-band sister size first.
Loose band sister size help
If the band rides up your back or feels loose by the end of the day, try the next tighter-band sister size.
Shopping another brand or size system
Use sister sizing only after you know your likely base size. It is especially useful when your exact size is out of stock or the brand runs tighter or looser than expected.
Common sister size families
These quick sister size examples help with shopping, comparing bra sizes, and understanding how nearby band-and-cup combinations relate to each other.
32D family
30DD ↔ 32D ↔ 34C ↔ 36B
34C family
32D ↔ 34C ↔ 36B
34D family
32DD ↔ 34D ↔ 36C
36D family
34DD ↔ 36D ↔ 38C
38DD family
36E ↔ 38DD ↔ 40D
40C family
38D ↔ 40C ↔ 42B
Most Indian brands are easier to compare in UK-style cup naming, but imported labels can still vary.
On marketplaces and imported bras, you may see labels like DDD instead of E. This tool normalizes common alternate labels so the page stays useful for India-first shoppers too.
Sister sizing is most useful when your exact size is out of stock, a brand runs unusually tight or loose, or you want a smarter next size to try before guessing randomly.
When sister sizing is not the real fix
Large cup wrinkling or cup gap that looks more like a shape mismatch than a simple band issue
Underwire pain, side poking, or center gore pain that suggests wire or cup problems
Obvious side spillage, quad-boob, or overflow that means the cups are likely not close enough
Jumping several sister sizes because one bra feels completely wrong in every way.
Use sister sizing only after you know what problem you are actually solving.
If the issue is really pain, gaping, shape mismatch, or spillage, the fit checker or fit-issues cluster is often more useful than another sister size step.
Use the fit checker first
Best when you are not fully sure whether the issue is really band tension, cup volume, or bra shape.
Recheck your measurements
Best when you have not measured recently, your body has changed, or most bras feel off lately.
Compare with a full size chart
Best when you want to understand UK, US, and India-friendly naming before shopping another brand.
What Is Sister Size?
Understand why cup letters change when the band changes.
Explore this next →
Signs Your Bra Fits Wrong
Use fit clues to decide whether sister sizing is enough or not.
Explore this next →
Band Riding Up
A loose band often needs a tighter sister size, not random guessing.
Explore this next →
Bra Size Calculator
Find your likely starting size first if you have not measured recently.
Explore this next →
FAQ
Sister size calculator FAQ
Common questions about sister bra sizes, tighter or looser band adjustments, cup volume, nearby bra sizes, and shopping different brands more confidently.
What is a sister size in bras?
A sister size is another bra size with similar cup volume but a different band size. For example, 34C, 32D, and 36B are nearby sister sizes.
Should I sister size up or down?
If the band feels too tight, go up one band size and down one cup letter. If the band feels too loose, go down one band size and up one cup letter.
How many sister sizes can I go?
Usually start with one sister size step. Going two steps away can sometimes work, but the fit often becomes less reliable, especially if the cups or bra shape already feel off.
Is 34C the same as 36B?
They are not identical, but they are nearby sister sizes with similar cup volume. The main difference is band fit: 36B feels looser in the band than 34C.
Can sister sizing fix every bra problem?
No. It mainly helps when the cup volume feels close but the band tension feels off. Wire pain, cup gap, shape mismatch, or side spillage may need a different fix.
Does sister sizing change across brands?
The logic stays the same, but real bras can still fit differently by brand, fabric, style, stretch, and shape. Sister sizing gives you a smarter starting point, not a perfect guarantee.
Why do some bras use DDD instead of E?
Some imported or marketplace bras use US-style labels like DDD instead of E. This tool normalizes common alternate labels so Indian shoppers can still compare nearby sister sizes more safely.
Is sister sizing useful when buying bras online in India?
Yes, especially when your likely starting size is out of stock or a brand runs tighter or looser than expected. It works best for one-step adjustments after you already know your base size.
Best way to use this tool
- Start from a bra size that already feels reasonably close in cup volume.
- Use one sister-size step first before you jump further away.
- Judge the new bra by band support, cup fit, comfort, and stability together.
- If the bra still gaps, spills, pokes, or feels strange, investigate shape and fit issues next.
Sister sizing has limits
Sister sizing is a practical bra size adjustment tool, but it cannot solve every issue. It works best when the cups already feel close and the real problem is band tightness, band looseness, or minor brand variation.
If the bra hurts, gaps badly, spills heavily, or feels wrong in shape, another sister size alone is usually not the full answer.
Next step
Need your main starting size first?
Sister sizing works best after you already have a likely starting size. Measure first, then compare nearby sizes with more confidence.
Open bra size calculator