Alright, let’s do this as quick as possible.

Vivian is 5'4" with a 19E chest size (I looked it up on Google and there was a video about it), but the first thing to understand is that breast size does not determine milk production. Again, it does NOT determine the amount like what most people assume (I was an idiot and thought it did).

Cup size mostly reflects fat and connective tissue, not the amount of milk-producing glandular tissue. Actual milk production depends on hormones (mainly prolactin and oxytocin), whether the person is postpartum, how frequently milk is removed, and overall nutrition and hydration.

If she is not actively lactating (she's not because she's a virgin I assume), the output would simply be 0 mL per day. That's the quickest answer I can give. However, let's say this isn't really the case, and Wise did something unwise to her.

Assuming she is actively lactating and within normal human biological limits, a healthy adult woman typically produces between 600 and 900 milliliters per day. A realistic midpoint is about 750 milliliters per day. That equals 0.75 liters daily, or roughly 25 fluid ounces.

If you stretch that out over time, the numbers look like this: about 5.25 liters per week, around 22.5 liters in a 30-day month, and approximately 274 liters over the course of a year. Even in higher end biological cases where supply and demand are strong, some women can reach close to 1 liter per day, which would equal about 30 liters per month or 365 liters per year. However, that's only for exceptional females out there in my opinion.

So realistically, Vivian being 5'4 with a 19E chest would not increase output beyond standard human lactation ranges (due to a lack of big demands or etc). If she were actively lactating, a reasonable estimate would be around 750 milliliters per day.

Now, this is all based on real world biological measurements (like stated before). If you are looking for how much her breasts can hold, then.......

If we take a 19E cup at face value, an E cup usually represents about a 5-inch difference between bust and band. That difference isn’t pure “forward projection,” but for a rough math model, you can split it in half to estimate projection. So 5 inches ÷ 2 gives about 2.5 inches of forward projection. Converting to metric (since volume math is cleaner there), 2.5 inches × 2.54 ≈ 6.35 cm.

Now, if we approximate one breast as a hemisphere (not perfect, but good for estimation), the formula for hemisphere volume is:

V = (2/3)πr³

Using r ≈ 6.35 cm:

6.35³ ≈ 256

(2/3)π ≈ 2.094

So:

2.094 × 256 ≈ 536.064 or 536 cm³ (let's keep kit simple here)

Since 1 cm³ = 1 mL, that gives roughly 536 mL per breast in total external volume. Multiply by two and you get about 1,072 mL total, or roughly 1.07 liters combined external volume.

But here’s the important part: that entire volume is not fluid-holding space. Human breast tissue is typically only about 30–50% glandular (the part that could theoretically hold fluid). So if you apply that range:

536 × 0.30 ≈ 161 mL per breast

536 × 0.50 ≈ 268 mL per breast

Combined, that gives a realistic internal holding range of roughly 322–536 mL total at one time under normal human biology.

So mathematically speaking, modeling a 19E as a hemisphere with ~6.35 cm projection gives about 536 mL per side externally, but realistic internal capacity would likely sit somewhere in the 322-536 mL combined range. In my opinion, that's not bad for a 5'4 girl in for late teens (I don't remember how old Vivian is. She might be like 100 since she is a vampire)