Can I mix these two RAM kits?
Adding RAM to a PC that already has some? Pick the two kits. You'll see what speed and timings they'll run at together and where it can go wrong.
Pick two kits to see how they'll run together. Add your motherboard to check slots and its speed limit too.
Mixing RAM: questions
Can I mix two different RAM kits?
Often yes, but it is never guaranteed. Kits are tested as sets, so two kits together, even with the same part number, can behave differently because the memory chips change between production batches. Expect to run both at the slower kit's speed and the looser kit's timings.
Can I mix RAM with different speeds?
Yes, but everything runs at the speed of the slower kit. A 3200 MT/s kit plus a 3600 MT/s kit gives you 3200 MT/s at best, and the XMP or EXPO profile of either kit may not be stable for both.
Can I mix 8 GB and 16 GB sticks?
It usually boots, but mixed stick sizes can break full dual-channel mode. On DDR4 many boards run part of the memory in single channel (flex mode). DDR5 boards are often less tolerant of mixed sizes.
Can I mix DDR4 and DDR5?
No. They use different slots with the notch in a different place, and a board supports only one of them.
Is it better to buy a new kit than to add sticks?
Usually yes. A single kit with the total capacity you want, such as 2x32 GB instead of two 2x16 GB kits, is tested as a set, runs at its rated speed more reliably and leaves slots free. Four DDR5 sticks in particular rarely reach their rated speed.