Hello,
I am building a new PC with :
Intel i9-13900K
Nvidia RTX 4090 FE
Samsung 990 Pro 2 Tb
NZXT H7 Flow case + Kraken Z73 watercooling 360 mm on top + 3 * 140 mm fans in front and 140 mm fan on the rear + 1000W PSU + upcoming N7 Z790 motherboard
I really don’t know how much RAM I should buy ? 32 or 64 ?
Thank you for your help
16 is sufficient for MSFS after SU5, before that it was more of a RAM hog. Go for 32 if you want to splurge (and it does seem like you want to splurge). 64 would likely gain you literally nothing compared to 32, even with ton of addons and background programs.
I have 64GB of RAM on my i9 10900K with an RTX 3080. Since the July 2021 update, the RAM use of MSFS has tanked. MSFS barely uses 10 to 12GB of RAM on my system.
It is my 3080 that is getting pushed on VRAM usage. Especially so with MSFS’s very poor VRAM usage in DX12. DX11 uses about 8GB of VRAM on my system whereas DX12 slurps up every bit of VRAM I have using around 9.8 to 9.9 GB. (I have a 2K monitor and run my graphics at 130 upscaling to keep the avionics displays nice and crisp.)
As expensive as DDR5 is these days you can either save some coin and get 32GB or if you might ever want 128GB RAM then invest today in 2 x 32 and get 64GB RAM. If it was me I’d just go with the 32GB RAM as I don’t think I am going to start rendering PIXAR movies at home. 
I’ve got 32 mb with an rtx 3080 and it’s plenty, Dx12 uses more than Dx11 but still gets nowhere near 32 mb.
If I go for 32 what’s best for performance : one stick of 32 or 2 sticks of 16.
32GB. Because why not RAM is relatively cheap these days. Sim runs in 16GB, but windows has nice headroom with 32GB, so browsers open with multi tabs for things like simbrief etc, and other apps like navigraph, fsltl etc. You can then quite happily alt-tab between fs and browser/desktop/other apps very smoothly. Not sure I’d expect that with only 16GB. 64GB is too much tbh although I have read that Windows uses RAM as cache, but I have no scientific evidence for that.
minimum amount of RAM for a new system in year 2022/23 is 32GIG and in my opinion its also the minimum to use MSFS without huge pageing, etc. ( MSFS can use 20gig an more ) . In case you can spend money for 64GIG, do it..
note: similar discussion
I would go for 32GB as recommended above and take the saving for an second m.2 so you can have the OS and msfs on separate storage.
Best is having 3 of them, one for OS, one for msfs and one for the caches and page files.
you not need pagefile if you own 64GIG.. ( but never disable it completly ! )
As mentioned in other topic, I own 64GIG RAM and I set pagefile to a minimum fallback of min 1gig and its never used. Exactly thats the reason why I mentioned “if enough money, go with 64GIG” and 32GIG is simple a minimum what each pc system should have this years.
get two sticks of 16. Make sure they are identical.
64GB here, I use a lot of external software, and 32GB limits me a lot.
When using RYZEN CPU, always use 2 or 4 sticks.
One stick is degrading performance, AMD Ryzen should always have dual channel ram to perform at it’s best…
Interesting, so does more ram help with having multiple programs open alongside msfs like fsltl and navigraph etc..? Or is that more a cpu thing?
Generally more apps = more RAM, for a smooth experience at least.
2x16 is good, use the last slots like A2 & B2
easy sayd: for all what not can hold in physical RAM, the usage of pagefile is necessary. That makes things slow ( it’s just a Disc-Drice and not RAM ) and of course the lifetime of your SSD will also reduced.
You not necessarly get higher fps with more RAM. It can be, but usually more RAM reduce loading time, reduce issues with pagefile usage, simple made all more fluid and stressfree.
And because 1 , 2 or 4 slots… Allways use even amount of Sticks so that Dual-Channel can be used ( and check the mainboard manual for correct slots ).
LOL
All that grunt and ask how much ram… Since your going b*lls to the wall as it is you may aswell go 64…
Just built a new machine with exactly same hardware you are using – 13900k and 4090. 32gb is fine BUT get the fastest memory you can. During the build I switched from 5600/CL36 to 6000/CL30 and was very surprised by how big the difference was in FS. Given the game is entirely CPU bound, I guess I should not have been surprised.
The memory speed definitely has a bigger impact than the extra 32gb.
with that huge 400Mhz difference , then 2fps more ? ..
All above 5600 is OC, so be carefull 
I actually cap @ 30FPS. I don’t think the 400MHZ made the difference—it was going from CL36 to CL30 which was big. The Passmark CPU scores went up more then 10%.
Still, it was the first time FS maintained 30FPS @ KLAX on 4K with Ultra settings and LOD @ 200.
And, to the point of the thread, the speed of the memory is more important than going from 32gb to 64gb.
if you first time need 64gig, because your system will slow-down becuase of e.g. paging, then we speak again
But of course, not buying the slowest RAM should be clear ( and yes, I know the timings are important ). But whether 2fps more is it worth, must users decide. I go with my next PC again with 64GIG RAM.
( I wonder: the new boards also support 7200 etc.. if OC then full OC 
)