EC2 Storage Requirement Calculator

volume size = (OS + application + daily data × retention days) × (1 + headroom); fleet cost = size × instances × price per GB-month. Retention is what turns a small daily write rate into the dominant term: 4 GB a day held for 45 days is 180 GB of steady state, far more than the OS and application together. Because EBS charges for provisioned rather than used capacity, headroom is a real cost — but volumes can be grown online with Elastic Volumes, so starting closer to the true requirement and expanding later is usually cheaper than sizing for year three on day one.

Day-one utilisation is deliberately low on a retention-driven volume, so a monitoring alert set on percent-used will fire months later when the window fills — plan the alarm around the steady state, not the initial footprint.

This calculator takes 7 inputs: Operating system and packages, Application and dependencies, Data written and retained per day, Retention window, Free-space headroom, Instances in the fleet, EBS price per GB-month. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.