AWS m7i.8xlargevsAWS m7i-flex.12xlarge

m7i.8xlarge pairs 32 vCPUs with 128GB of RAM at $1.6128/hr On-Demand (about $1161/mo at 24×7). m7i-flex.12xlarge pairs 48 vCPUs with 192GB at $2.2982/hr (~$1655/mo). m7i.8xlarge is 42% cheaper per hour than m7i-flex.12xlarge ($0.6854/hr gap).

Because both instances are in the **m7i 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: m7i.8xlarge gives you 32 vCPUs and 128GB of RAM, m7i-flex.12xlarge gives you 48 vCPUs and 192GB. 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 m7i.8xlarge delivers ~62% more single-thread Sysbench score per dollar (2003 vs 1234 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 (50282 vs 68078) are what to weigh. Spot pricing flips many of these comparisons — when m7i.8xlarge drops to $0.6310/hr and m7i-flex.12xlarge drops to $0.7997/hr, the cheap-per-hour winner can swing meaningfully.

In practice, pick m7i.8xlarge when your workload is closer to general-purpose (balanced general-purpose workloads with a 1:4 vCPU-to-memory ratio). Pick m7i-flex.12xlarge when it's closer to general-purpose (balanced general-purpose workloads with a 1:4 vCPU-to-memory ratio). 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.