AWS i3en.12xlargevsAWS i3en.3xlarge

i3en.12xlarge pairs 48 vCPUs with 384GB of RAM at $5.4240/hr On-Demand (about $3905/mo at 24×7). i3en.3xlarge pairs 12 vCPUs with 96GB at $1.3560/hr (~$976/mo). i3en.3xlarge is 75% cheaper per hour than i3en.12xlarge ($4.0680/hr gap).

Because both instances are in the **i3en family**, the only thing that changes between them is sizing — same silicon, same architecture (Intel Xeon (x86_64)), same burstable/sustained behavior. The choice is purely about how much capacity you actually need: i3en.12xlarge gives you 48 vCPUs and 384GB of RAM, i3en.3xlarge gives you 12 vCPUs and 96GB. AWS scales pricing close to linearly within a family, so picking the right size is mostly about right-sizing your workload, not getting a better deal per vCPU.

On raw price-per-performance, the two are i3en.3xlarge delivers ~284% more single-thread Sysbench score per dollar (210 vs 806 points per $1/hr). That's the cleanest signal we have for "which one runs your workload faster per dollar," but it only matters if your workload is single-thread-bound; for parallel workloads the multi-core scores (39280 vs 10075) are what to weigh. Spot pricing flips many of these comparisons — when i3en.12xlarge drops to $1.5683/hr and i3en.3xlarge drops to $0.4664/hr, the cheap-per-hour winner can swing meaningfully.

In practice, pick i3en.12xlarge when your workload is closer to storage-optimized (NVMe SSD) (I/O-bound work needing low-latency NVMe local storage — NoSQL, search). Pick i3en.3xlarge when it's closer to storage-optimized (NVMe SSD) (I/O-bound work needing low-latency NVMe local storage — NoSQL, search). When neither side is obviously right, the cheaper hourly rate usually wins for fault-tolerant batch workloads, while the higher single-core score usually wins for latency-sensitive web traffic. The regional pricing tables linked from each instance page below show where each is currently cheapest — sometimes a >20% regional gap flips the comparison entirely.