Breast Weight Calculator
How much do boobs weigh? Rather than looking your cup letter up in a table - which cannot work, because a 28D and a 40D are not the same amount of tissue - this estimates the volume from your own two measurements and converts it at a measured tissue density.
The pair, together
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How that was worked out
- Extra circumference over the bust
- Modelled breast base and projection
- Volume per breast
- Tissue density used
- 0.95 g/mL
This is an estimate, not a measurement, and you get a range because breast volume genuinely varies between people - published averages differ by about double. No arithmetic removes that. Density plays a part too: glandular tissue is heavier than fatty tissue. What the estimate is good at is the gap between two sizes, because that is fixed by how bras are made. Where you sit inside the range depends on your body.
Why a cup letter alone cannot tell you the weight
Almost every page that answers this question hands you a chart with a cup letter down one side and a weight down the other. The charts disagree with each other wildly - for a single D-cup breast we found published figures of 425 g, 500 g, 680 g and 860 g - and they disagree because the question they are answering is underspecified. A cup letter is not a volume. It is the difference between a bust and a band, so the same letter on a different band is a different amount of tissue.
Run it through: a 28D is four inches of difference on a small ribcage and comes out around 252 g per breast. A 40D is the same four inches on a much larger frame and comes out around 1050 g. Both are D cups. One is more than 4 times the other.
The model, in full
There is no secret to it, and it is worth being able to check rather than trust.
- Your two measurements say how much bigger your bust is than your ribcage, and how big your ribcage is. Both matter - the same cup letter on a bigger band is more tissue.
- Going up one cup size adds a roughly fixed amount, and it has been measured: about 140 mL. That figure holds whether you are going from B to C or from F to FF.
- A larger breast also sits on a wider base rather than only sticking out further, so the shape grows in every direction at once.
- That shape is then checked against your own two measurements. A breast cannot stand out further than your bust measurement leaves room for, so on a small cup and a wide frame it comes out flatter and wider. Only up to a point, though: past it the estimate comes down instead, which is why the smallest cups weigh much less here than their size alone would suggest.
- Weight follows from volume at 0.95 g/mL, the middle of the range measured for breast tissue.
The part we are sure about is the gap between two sizes. Where the whole scale sits is a different question, and the honest answer is that it varies a lot between people - published averages differ by about double. That is why this page gives you a range instead of one confident number.
Sister sizes come out identical, by construction
Sister sizes are meant to hold the same amount on different bands, and that is exactly how bras are made - a 36D cup and a 38C cup are built to the same size. So they come out identical here, which is the point: if they did not, one of us would be wrong.
| Size | Per breast | Volume |
|---|---|---|
| 30DDD | 651 g | 685 mL |
| 32DD | 651 g | 685 mL |
| 34D | 651 g | 685 mL |
| 36C | 651 g | 685 mL |
The same figure four times, because that is what a sister size is. Note what this is and is not: the model is built on the assumption that sister cups match, so its agreeing is a consistency check rather than proof. The reason to believe it is that bras are graded that way when the pattern is cut.
Reference: weight per breast by band and cup
Generated from the same model, in grams per breast, with the weight of the pair in kilograms underneath. Read across a row to see what a cup letter costs; read down a column to see how much the band matters.
| Band | B | C | D | DD | DDD / E | G / F |
|---|---|---|---|---|---|---|
| 30 | 119 g0.2 kg pair | 252 g0.5 kg pair | 385 g0.8 kg pair | 518 g1.0 kg pair | 651 g1.3 kg pair | 784 g1.6 kg pair |
| 32 | 252 g0.5 kg pair | 385 g0.8 kg pair | 518 g1.0 kg pair | 651 g1.3 kg pair | 784 g1.6 kg pair | 917 g1.8 kg pair |
| 34 | 385 g0.8 kg pair | 518 g1.0 kg pair | 651 g1.3 kg pair | 784 g1.6 kg pair | 917 g1.8 kg pair | 1050 g2.1 kg pair |
| 36 | 518 g1.0 kg pair | 651 g1.3 kg pair | 784 g1.6 kg pair | 917 g1.8 kg pair | 1050 g2.1 kg pair | 1183 g2.4 kg pair |
| 38 | 651 g1.3 kg pair | 784 g1.6 kg pair | 917 g1.8 kg pair | 1050 g2.1 kg pair | 1183 g2.4 kg pair | 1316 g2.6 kg pair |
| 40 | 775 g1.6 kg pair | 917 g1.8 kg pair | 1050 g2.1 kg pair | 1183 g2.4 kg pair | 1316 g2.6 kg pair | 1449 g2.9 kg pair |
US cup letters on top, UK equivalents beneath. They diverge above DD - a UK E is a US DDD.
What the number means once you have it
Two and a half kilograms is roughly a full 2.5 litre bottle of water, carried on the front of the ribcage all day, on a lever arm that the spine has to counterbalance. The band of a well-fitted bra takes around 80% of that around the ribcage, where the load is close to the body's centre line. The straps take the remainder.
When the band is too loose - which is what the +4 method reliably produces - that ratio inverts. The straps end up carrying most of the weight on two narrow strips over the trapezius, and that is where strap grooving, upper-back ache and the reflex of hooking your thumbs under the straps all come from. The heavier the estimate this page gives you, the more the band size is the thing worth getting right.
For running and other impact activity the relevant figure is not the static weight but what it does under acceleration - vertical displacement of several centimetres per stride, at several times body-weight-equivalent force at the point of the breast. A pair estimated at 1 kg is not a 1 kg problem when you run.
Honest limits
Where this estimate is weakest
A geometric model has to assume a shape, and no real breast is that shape. These are the four cases where the number this page gives you will be furthest out, and in which direction.
Very soft or pendulous tissue
The model assumes the breast projects forward from the chest wall. Tissue that hangs downward puts the same volume in a different place, and the standing bust measurement under-reads it. Measure leaning forward as well and treat the larger figure as the upper bound.
Dense glandular tissue
Density near 0.98 rather than 0.95 g/mL adds about 3% - small next to the geometric error, but it stacks in the same direction for younger measurements, since reported density falls slightly with age.
Breasts of noticeably different sizes
The model halves a single circumference surplus between two breasts. If yours differ by a cup size, the true split is nearer 60:40 than 50:50, so neither breast weighs exactly what the page says - the total for the pair stays about right.
Implants
Silicone is denser than breast tissue, at roughly 1.1 g/mL against 0.95. An augmented breast weighs more than this page will tell you, and the gap widens with implant size.
Related
- The bra size calculator - the same two measurements, turned into a band and cup instead of a weight.
- Sister sizes - the sizes that hold the volume this page just estimated.
- What DD actually means, and what it weighs.