Have you ever noticed

[@llli*toddlerandtwins]

I find my medela bottles (that came with my lactina collection kit) measure higher than when I pour my milk into my evenflo bottles. 5oz turns into 4oz. Always found that frustrating. I suppose the medela could be right and the evenflo wrong. Glad I am not the only one who found a difference!

[@llli*mek]

I have noticed this too! The NUK bottles measure slightly higher than the Playtex ones that we have. So, on days where I've pumped a *little* less, I send the milk to daycare in NUK bottles, so that it looks like the same amount.

[@llli*toddlerandtwins]

I have noticed this too! The NUK bottles measure slightly higher than the Playtex ones that we have. So, on days where I've pumped a *little* less, I send the milk to daycare in NUK bottles, so that it looks like the same amount.

[@llli*scienceteachermommy]

Apparently the specific gravity of mature human milk is 1.031, which makes its density 1.031 g/mL. Since 1 fluid oz is 29.6 mL, 4 oz should be 122g. Since the density of BM is so close to that of water, you could reasonably go with 4 fluid oz = 4 weight oz.

I might have to get out the kitchen scale when I make up bottles tonight. I do usually go with the markings on the Medela bottles; it would be interesting to see the variation simply filling the same types of bottles.

I really nerded up this discussion, didn't I?!

[@llli*joe.s.mom]

I would have guessed, with its high fat content, that breastmilk would weigh less than water. But what do I know?

[@llli*persephone-ashes]

I hate all the measuring. I know you're supposed to be able to pump into the medela storage bags, but I can't ever do it. I pump into bottles, then poor in the bags, and the measurements on the bag never match (even closely) to the bottle. I've tried trying to squeeze the bag to make sure that there aren't any unutilized corners or anything, but still no luck.

man it'd be easier to no have to pump!

[@llli*phi]

Apparently the specific gravity of mature human milk is 1.031, which makes its density 1.031 g/mL. Since 1 fluid oz is 29.6 mL, 4 oz should be 122g. Since the density of BM is so close to that of water, you could reasonably go with 4 fluid oz = 4 weight oz.

I might have to get out the kitchen scale when I make up bottles tonight. I do usually go with the markings on the Medela bottles; it would be interesting to see the variation simply filling the same types of bottles.

I really nerded up this discussion, didn't I?!

But density is temperature dependent, right? How might that influence your results? It's been forever since I took fluid dynamics, and honestly it was not one of my favorite classes so I'm not going to try to tackle this one. Maybe try a bottle of cold milk and a bottle at room temperature to see if it makes any difference.

I'm interested to hear your results though.

[@llli*sassypants]

Erin and my husband would get along He has used our kitchen scale for his own home "experiments" on many occasions.

The temperature difference between 40F milk and 70F milk would make negligible difference in density. I am an engineer and we round everything, but the scientist started that trend by making the assumption that we could reasonably use the properties of water. My kitchen scale only gets down to the 1/8th of an ounce anyway.

[@llli*scienceteachermommy]

But density is temperature dependent, right? How might that influence your results? It's been forever since I took fluid dynamics, and honestly it was not one of my favorite classes so I'm not going to try to tackle this one. Maybe try a bottle of cold milk and a bottle at room temperature to see if it makes any difference.

I'm interested to hear your results though.

The difference in density in water from 30 C and 0 C is less than 1%, which, I would expect, is less than the error inherent in a kitchen scale. When I have done this as a lab experiment, both as a student and as a teacher, the students have looked up the density of water at the temperature of the room.

The difference in density with temperature is definitely smaller than the error in filling the bottles.

[@llli*scienceteachermommy]

I would have guessed, with its high fat content, that breastmilk would weigh less than water. But what do I know?

Ah, but you forgot the milk solids! This article looks at the density of cow milk and even has an equation for the density of milk based upon the percentage of fat and milk solids. Human milk appears to fall in the same range as cow milk in terms of density.

(This, BTW, is what is referred to as advanced grading avoidance. Next thing you know I will start cleaning my classroom, which I do actually need to do considering I am moving out of it at the end of the week.)

Now, back to your regularly scheduled nerdiness.