Hydro Flasks are great at keeping your water cold and you're coffee hot but if you're anything like me and you're driving around a fair bit you likely want to get a Hydro Flask size that fits in the cup holder of your car.
So what are the best Hydro Flask sizes that fit in a cup holder and what sizes simply won't fit?
The standard mouth Hydro Flasks (18 oz, 21 oz + 24 oz) are the thinnest type of Hydro Flask and will fit into any standard cup holder. The wide mouth 12 oz and 20 oz are a tiny bit wider but should still fit. The 32 oz and 40 oz Hydro Flask are too thick and will NOT fit in a cup holder.
It depends on what car make/model you have and how big your cup holders are.
In my smaller car the cup holder could only fit the standard mouth Hydro Flask and not a wide mouth Hydro Flask which is only a tiny bit wider.
In my girlfriends car the wide mouth fit easily in her main cup holders but didn't fit in the cup holders in the back.
In pretty much every car my 32 oz Hydro Flask did NOT fit in any cup holders.
What Hydro Flask Sizes Fit In a Standard Car Cup Holder?
I personally looked into the widths/diameters of every different Hydro Flask size in order to create my Hydro Flask sizes chart.
I also own an 18 oz standard mouth Hydro Flask and a 12 oz wide mouth kids Hydro Flasks and was able to test if Hydro Flasks fit in my cup holders.
Below you can see the diameters of each of the different types of Hydro Flasks on the market.
Standard Mouth (18, 21, 24oz): 2.87 inches (7.23 cm)
Wide Mouth (12, 16, 20 oz): 2.91 inches (7.39 cm)
25 oz Wine: 3.1 inches (7.87 cm)
Wide Mouth Large (32, 40 oz): 3.58 inches (9.09 cm)
64 oz Wide Mouth + Growler: 4.72 inches (11.98 cm)
Oasis (64, 128 oz): 5.8 inches (14.73cm)
If you have a car with small cup holders then get a standard mouth Hydro Flask as this is the most likely to fit.
If you have decent sized cup holders then get a standard mouth or a wide mouth Hydro Flask. Basically any size from 12 oz up to 24 oz is fine.
No car cup holders will fit Hydro Flasks above 32 oz without an adapter.
For Larger Sizes Consider a Cup Holder Expander
A cup holder expander like the Smart Kup is something that goes in your regular car cup holder but has a wider cup holder at the top.
This turns your regular small car cup holder into an extra large cup holder big enough to fit your 32 oz or 40 oz Hydro Flask.
I've done a full write up of the best Hydro Flask cup holder adapters if you want to get one of these and don't know which one to choose. But honestly, they are all pretty good and the most simple ones are often the best.
I personally like the PFCC Cup Holder Expander as the base is adjustable so it fits perfectly in your cup holder and won't fall out and it has rubber tabs on the top to hold in your Hydro Flask nice and tight.
Best Hydro Flask Size For Cup Holders: Standard Mouth 18, 21 and 24 oz
The best Hydro Flasks for cup holders are the standard mouth Hydro Flasks as these have the thinnest profile and fit into almost all standard sized cup holders.
They have a width of 2.87 inches (7.23 cm) and this is just small enough to even fit into small cup holders.
Although when I tried to fit it into the back seat of my girlfriend's car you can see that it only JUST fit it and didn't make it all the way down to the bottom.
There are 3 sizes of the standard mouth Hydro Flasks.
The 18 oz is the smallest and shortest size and in my opinion is the best Hydro Flask that fits into cup holders.
The 21 oz and 24 oz are obviously bigger in size but this makes them taller and the 24 oz can sometimes be too
Also Good For Cup Holders: Wide Mouth Hydro Flasks 12, 16, 20 oz
The Wide Mouth Cup Holders are only slightly wider that the standard mouth by a fraction of an inch and can also fit in most car cup holders.
At 2.91 inches (7.39 cm) it's only 0.04 inches (0.16 cm) wider than the standard mouth Hydro Flasks. But strangely enough when I looked at if Hydro Flasks fit in cup holders this tiny little increase in size made the difference between if the Hydro Flask fit in the smaller cup holders or not.
The wide mouth Hydro Flasks fit well in all the standard adult sized cup holders, it only struggled in the smaller kids sized cup holders.
Below you can see me trying to fit a 12 oz wide mouth Hydro Flask into the cup holder at the back of my car.
This is an especially small cup holder and it only just didn't fit. The 18 oz just squeezed in here as it was a tiny but smaller but that little difference in width meant that in this case the wider Hydro Flask didn't fit.
Won't Fit In Cup Holders: 32 + 40 oz
The 32 oz and the 40 oz are the most popular Hydro Flask sizes according to the data I could find as well as a poll I have on this website.
Take your vote below of what size Hydro Flask you have or want to get and you can see the results.
However, while the 32 oz and 40 oz are great sized Hydro Flasks and very popular they unfortunately don't fit in cup holders. You would need to get an extra large cup holder expander if you want to be able to fit these sizes into a cup holder.
Fit Great In Cup Holders: Hydro Flask Tumblers
Hydro Flask tumblers are some of the biggest sized Hydro Flasks to fit in a cup holder.
This is because they are wider at the top and thinner at the bottom.
The base of the 16 oz, 22 oz and 32 oz are all the same at 2.9 inches (7.37 cm).