I have put together this little guide to help give you all an idea of which size cooler to choose when you are going to ship breastmilk.
It is important to point out that there is no way to guarantee that a certain cooler will perfectly fit X number of ounces of milk. The amount of milk that a cooler will hold depends on several factors - how the milk is frozen (flat or not), whether or not you are using dry ice(and how much of it), and how the cooler is packed.
Unfortunately, choosing the right size cooler is more of a guessing game than an exact science. However, I can share with you what has worked for me over several shipments of milk. I think I have a fairly decent handle on things at this point, so this should be relatively accurate.
Let me also take this moment to remind you that if you are shipping less than 300oz of milk, you absolutely, positively MUST use dry ice. It doesn't matter if you are shipping overnight. Anything less than 300oz (500oz in summer) is too risky to send without it.
During the summer months, I recommend using dry ice on all shipments under 600oz that will be in transit for more than one day. As always, make sure the coolers are packed properly with as little extra airspace as possible.
For up to 500oz of milk, I recommend this cooler:
Mr.Box Online - Superior Cooler
In my experience, this cooler can hold up to 550oz of milk (if frozen flat, closer to 500oz otherwise). If you are sending a smaller amount, this cooler may seem big, but keep in mind the need for dry ice. You will need the extra space. Just make sure to fill the rest with paper.
For 1 day shipping, use at least 5-8lbs of dry ice. For 2 day shipping, at least 10-15 lbs.
For up to 1000oz of milk, I recommend this cooler:
Mr.Box Online - Extra Large Cooler
In my experience, this cooler can hold up to 1000oz of milk (frozen flat, closer to 900 otherwise). 900oz will generally keep itself nice and cold without dry ice, but in the warmer months, it's always safest to include some dry ice.
For 1 day shipping, use at least 8-10lbs of dry ice, for 2 day shipping, use at least 15lbs of dry ice.
For up to 1400oz of milk, I recommend this cooler:
MrBox Online - Jumbo Cooler
Laura and I used this cooler once. She shipped me 1300oz of milk, frozen flat. There was still room for 4-6 boxes of baby cereal, which she used for insulation.
Be warned that a cooler this size filled with frozen milk is extremely heavy. I believe our shipment weighed in at around 100lbs.
If using dry ice, I recommend at least 15lbs. However, when Laura shipped this to me, she sent it 2-day and UPS lost the package. It ended up being in transit for 6 days, rather than 2. I was worried sick, but when the package finally arrived, all of the milk was still frozen solid - even the fresh milk she had packed in there at the last minute froze. The more milk you ship at once, the safer your shipment is without dry ice. But bear in mind, this shipment took place in the winter time. I don't think we would have had such a happy outcome had it been summer.
Remember that when you ship breastmilk, there are all sorts of things that come into play: transit time, the weather, how the milk has been packed, etc. It's always best to spend the extra money to err on the side of caution (i.e. shorter shipping time, using dry ice) to avoid losing a shipment of precious breastmilk for your baby.