AWS c3.4xlargevsAWS c3.8xlarge

c3.4xlarge pairs 16 vCPUs with 30GB of RAM at $0.8400/hr On-Demand (about $605/mo at 24×7). c3.8xlarge pairs 32 vCPUs with 60GB at $1.6800/hr (~$1210/mo). c3.4xlarge is 100% cheaper per hour than c3.8xlarge ($0.8400/hr gap).

Because both instances are in the **c3 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: c3.4xlarge gives you 16 vCPUs and 30GB of RAM, c3.8xlarge gives you 32 vCPUs and 60GB. 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 c3.4xlarge delivers ~100% more single-thread Sysbench score per dollar (1257 vs 627 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 (12945 vs 25860) are what to weigh. Spot pricing flips many of these comparisons — when c3.4xlarge drops to $0.3110/hr and c3.8xlarge drops to $0.5585/hr, the cheap-per-hour winner can swing meaningfully.

In practice, pick c3.4xlarge when your workload is closer to compute-optimized (CPU-bound work — batch processing, web servers under sustained load, game servers). Pick c3.8xlarge when it's closer to compute-optimized (CPU-bound work — batch processing, web servers under sustained load, game servers). 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.