RDS Storage Calculator
Size an RDS volume from current data, growth rate and free-space headroom, and see the monthly storage cost.
About RDS Storage Calculator
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
Worked example
With the default values below, RDS Storage Calculator returns Recommended Allocated Storage of 780. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Current data sizeaccepts 0–65,536 GB
- 320 GB
- Data growthaccepts 0–5,000 GB/month
- 25 GB/month
- Plan aheadaccepts 1–60 months
- 12 months
- Free space to keepaccepts 0–80 %
- 20 %
- Storage priceminimum 0 $/GB-month
- 0.115 $/GB-month
Results
- Recommended Allocated Storage
- 780 GB
- Projected Data Size
- 620 GB
- Projected Data Size
- 620 GiB
- Monthly Storage Cost
- $89.70
- Months Until the Volume FillsReported as 0 when the growth rate is left at zero.
- 18.4
Step by step
- 1Values used
- 2RDS Storage
- 3Recommended Allocated Storage= 780 GB
- 4Projected Data Size= 620 GB
- 5Projected Data Size= 665,719,930,880
- 6Monthly Storage Cost= 89.70
- 7Months Until the Volume Fills= 18.4
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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.