20GB works in most laptops.

Yes, you can put a 16GB stick in the single slot alongside the soldered 4GB for a total of 20GB. Most modern laptops support asymmetric dual-channel mode, so you get the speed benefit where both channels match (4+4GB = 8GB in dual-channel, the remaining 12GB runs single-channel). That’s fine for everyday tasks and even light gaming.

The only real gotcha: check your laptop’s official spec sheet or community forums. Some ultra-budget models or very old BIOS versions get fussy about odd totals. But in my experience, it works way more often than it doesn’t. Worst case, you return the stick.

One thing to know: if your motherboard supports dual-channel at all, it usually adapts. The performance hit from the asymmetric part is rarely noticeable outside of memory-intensive workloads like video editing. For web browsing, Office, and coding? You’ll be fine.