Size an RDS volume from current data, growth rate and free-space headroom, and see the monthly storage cost.
RDS bills the allocated volume size, so the volume must cover projected data plus the free space the engine needs for autovacuum, index rebuilds, temporary tables and sort spills. Dividing by (1 − headroom) rather than adding a flat percentage gives a volume where the free space is the requested fraction of the whole volume, and rounding up to 10 GB keeps the number tidy for storage autoscaling steps. The storage rate is an editable input with a realistic us-east-1 default — confirm the current price with AWS for your region and volume type. An RDS volume can be grown online but not shrunk without a dump and reload, so under-sizing costs an outage and over-sizing is a bill you pay every month for capacity you never use.
RDS Storage
projected data = current + growth × months; allocated = round up to 10 GB of projected ÷ (1 − headroom fraction), with a 20 GB floor.
projected data = current + growth × months; allocated = round up to 10 GB of projected ÷ (1 − headroom fraction), with a 20 GB floor. RDS bills the allocated volume size, so the volume must cover projected data plus the free space the engine needs for autovacuum, index rebuilds, temporary tables and sort spills. Dividing by (1 − headroom) rather than adding a flat percentage gives a volume where the free space is the requested fraction of the whole volume, and rounding up to 10 GB keeps the number tidy for storage autoscaling steps. The storage rate is an editable input with a realistic us-east-1 default — confirm the current price with AWS for your region and volume type.
An RDS volume can be grown online but not shrunk without a dump and reload, so under-sizing costs an outage and over-sizing is a bill you pay every month for capacity you never use.
This calculator takes 5 inputs: Current data size, Data growth, Plan ahead, Free space to keep, Storage price. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Autoscaling is a safety net, not a plan — it only triggers below roughly 10% free space, adds capacity in large steps and cannot shrink afterwards. Size the volume deliberately and keep autoscaling as the backstop with a maximum threshold set.