Can I install more RAM on my 2019 iMac 27in?

Are you wanting more RAM because your iMac is slow? Long history teaches that 95% of slow iMac compaints here are due to a slow mechanical hard drive or, for 2019 27" models like yours, a malfunctioning Fusion (hybrid) drive.

If either is the case, no amount of additional RAM will heal that.

A properly functioning Apple Fusion drive is faster that the cheapest external SSD option but slightly slower than the more expensive ThunderBolt 3/4 external options. But we need to know if your current storage option, be it Fusion of factory SSD, is contributing or if something else is afoot.

If this is a "slow" issue, and you wish a machine-specific, data-driven evaluation in this setting where we can neither see nor touch your computer, please post an EtreCheck report. We can quickly and within the limitations of these forums help you determine what issues are at play without our playing a protracted game of "20 Questions" with you that could go on for days. 

EtreCheck Pro is available here:

https://etrecheck.com/index

The free version will do nicely for this purpose, although the app is worthy of our financial support.

We can see hard data about drive performance, software issues and interferences, and RAM usage including RAM starvation. Etrecheck is the development of a long-serving and trusted ASC contributor. It is a reporting app, not a "fix-it” app, expressly for displaying information in these forums to help us help you remotely. It will not reveal any personal or secure information.

Please see this excellent user tip on how to post long text reports like EtreCheck's into a forum response:

How to use the Add Text Feature When Post… - Apple Community

RAM won't resolve speed issues. Please do what Allan Jones recommended and download and run Etrecheck. 

Copy the report

and use the Additional Text button to paste the report in your reply.

Then we can examine the report and see if we can determine the cause of the problem.

MPBaldwin wrote:

How much RAM can I put into my 2019 27 inch iMac? Is there a limit to how much is worthwhile?

The need for additional RAM varies on the amount that is currently installed and the RAM pressure.

To check your RAM pressure, open your iMac's Activity Monitor and select the Memory tab.

If the memory graph is running green, then you really do not need any additional RAM.

If the memory graph is running orange, then adding a couple of 8GB modules will be plenty.

If the memory graph is running red, then adding a couple of 8GB modules or 16GB modules will be plenty.

For additionally RAM modules, I recommend only purchasing from trusted suppliers like Crucial or OWC.

https://www.crucial.com/compatible-upgrade-for/apple/imac-(retina-5k--27-inch--2019)-imac-19-1

https://eshop.macsales.com/shop/memory/imac-2019-27-inch

My 2020 iMac has 128GB. It was more a “want” than a “need”. I think you’ll do just fine with 64GB. There’s so few use cases for 128GB over 64GB for most folks.

as you haven’t mentioned what you have now, and if your current configuration is using 2 or 4 memory slots, you could just get 2 32GB cards and insert them to add that much more over your current amount.

Do not use RAM from OWC for these iMacs. Use RAM from Crucial as the chips are made by OEM Apple supplier.

I had a nightmare with OWC when upgrading my iMac. It did not play well and both OWC and Apple kept finger-pointing each other. Crucial worked first-time.

that iMac can use up to 128 GB of RAM. depending on what you use it for, 128 GB is very likely way overkill. as a matter of fact, I have installed 64 GB into my (similar) iMac, and it is way more than I ever needed.

also, if you are thinking of a RAM upgrade to speed up the Mac, you might want to determine if your Mac is HDD based. if it is, you would get a much greater performance jump by swapping out the HDD for an SSD. but that is an operation that I would recommend a professional installation.

alternatively, you could get an external SSD and run macOS from that drive. to implement that, please see Use an external SSD as your startup disk with your iMac or Mac mini - User Tip

How much and what type of RAM that iMac supports, you can probably find at https://support.apple.com/docs.

In general, I'd say that you should install the maximum amount of RAM that is supported and that you want to spend the money for.

But on that "old" hardware your main issue will be other restrictions, like no more macOS updates or lack of app support.

ebbelwoi wrote:

But on that "old" hardware your main issue will be other restrictions, like no more macOS updates or lack of app support.

FWIW, while that iMac will likely not be upgradeable past Sonoma, it will likely still receive Sonoma updates until the fall of 2026.