EC2 Memory Utilization Calculator
Work out real memory utilisation after OS overhead, the GB per vCPU ratio, and the memory a target utilisation needs.
Inputs
EC2 does not publish memory metrics — this comes from the CloudWatch agent or your own exporter.
Memory Utilisation of Usable RAM
31.1%
Memory Still Available
21.0GB
Memory per vCPU
4.00GB/vCPU
Memory Needed at the Target
15GB
Memory Beyond the Target
17.0GB
Matching Instance Family
General purpose shape — about 4 GB per vCPU
Step by step
Values used
Instance memory = 32 GB; vCPUs on the instance = 8 vCPU; Memory used by the workload = 9.50 GB; Operating system and agent overhead = 1.50 GB; Target memory utilisation = 75 %
EC2 Memory Utilization
usable RAM = instance memory − OS overhead; utilisation = used ÷ usable; memory needed = used ÷ target + overhead.
Memory Utilisation of Usable RAM
= 31.1
Memory Still Available
= 21.0 GB
Memory per vCPU
= 4.00 GB/vCPU
Memory Needed at the Target
= 15 GB
Memory Beyond the Target
= 17.0 GB
Matching Instance Family
= General purpose shape — about 4 GB per vCPU
How it works
Utilisation should be measured against usable memory, not the marketing figure, because the kernel, page cache and agents claim a fixed slice before your process starts. The GB-per-vCPU ratio then tells you which family you are on — roughly 2 for compute optimised, 4 for general purpose and 8 for memory optimised — so a workload sitting at 4 GB per vCPU with spare CPU is a candidate to move to an R-family shape with fewer, larger-memory cores. Memory is the one EC2 dimension CloudWatch cannot see by default, so it is where over-provisioning hides — and unlike CPU, running out of it kills the process rather than slowing it down.
Formula
EC2 Memory Utilization
usable RAM = instance memory − OS overhead; utilisation = used ÷ usable; memory needed = used ÷ target + overhead.
- usable RAM
- Memory left for the workload after the OS and agents
- memory per vCPU
- The ratio that identifies the instance family
- target
- Utilisation ceiling you want to leave room under
Frequently Asked Questions
How is EC2 Memory Utilization calculated?
usable RAM = instance memory − OS overhead; utilisation = used ÷ usable; memory needed = used ÷ target + overhead. Utilisation should be measured against usable memory, not the marketing figure, because the kernel, page cache and agents claim a fixed slice before your process starts. The GB-per-vCPU ratio then tells you which family you are on — roughly 2 for compute optimised, 4 for general purpose and 8 for memory optimised — so a workload sitting at 4 GB per vCPU with spare CPU is a candidate to move to an R-family shape with fewer, larger-memory cores.
Why does EC2 Memory Utilization matter?
Memory is the one EC2 dimension CloudWatch cannot see by default, so it is where over-provisioning hides — and unlike CPU, running out of it kills the process rather than slowing it down.
What values do I need to enter?
This calculator takes 5 inputs: Instance memory, vCPUs on the instance, Memory used by the workload, Operating system and agent overhead, Target memory utilisation. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
You might also need
- EC2 Instance Right-Sizing CalculatorCommonly used together
- EC2 CPU Utilization CalculatorCommonly used together
- EC2 Instance Density CalculatorCommonly used together
- EC2 Instance Cost CalculatorAlso in AWS Compute
- Reserved Instance Savings CalculatorAlso in AWS Compute
- EC2 Boot Time CalculatorAlso in AWS Compute