RDS Storage Calculator
Size an RDS volume from current data, growth rate and free-space headroom, and see the monthly storage cost.
Inputs
Index rebuilds, vacuum and temp files need free space on the volume.
gp3 about $0.115/GB-month, io1 about $0.125, magnetic about $0.10 in us-east-1.
Recommended Allocated Storage
780GB
Projected Data Size
620GB
Projected Data Size
620 GiB
Monthly Storage Cost
$89.70
Months Until the Volume Fills
18.4
Reported as 0 when the growth rate is left at zero.
Step by step
Values used
Current data size = 320 GB; Data growth = 25 GB/month; Plan ahead = 12 months; Free space to keep = 20 %; Storage price = 0.1150 $/GB-month
RDS Storage
projected data = current + growth × months; allocated = round up to 10 GB of projected ÷ (1 − headroom fraction), with a 20 GB floor.
Recommended Allocated Storage
= 780 GB
Projected Data Size
= 620 GB
Projected Data Size
= 665,719,930,880
Monthly Storage Cost
= 89.70
Months Until the Volume Fills
= 18.4
How it works
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.
Formula
RDS Storage
projected data = current + growth × months; allocated = round up to 10 GB of projected ÷ (1 − headroom fraction), with a 20 GB floor.
- current
- Size of the data files today, not the volume size
- headroom
- Share of the volume deliberately left empty
- allocated
- Provisioned volume size — this is what RDS bills
Frequently Asked Questions
How is RDS Storage calculated?
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.
Why does RDS Storage matter?
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.
What values do I need to enter?
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.
Should I just enable storage autoscaling instead?
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.