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Cache Node Sizing Calculator

Work out cache node sizing instantly with clear inputs, formula shown and shareable results.

About Cache Node Sizing Calculator

Cache sizing reserves memory for the share of the working set you want resident, then divides by usable memory per node — around 75 percent of nominal, because Redis needs headroom for replication buffers, fragmentation and background saves. Replicas multiply node count without adding cache capacity, since they hold the same data.

Formula

Cache sizing

memory needed = working set x target hit rate; usable per node = node memory x 0.75; shards = ceil(needed / usable); nodes = shards x (1 + replicas)

Worked example

With the default values below, Cache Node Sizing Calculator returns Cache nodes required of 6. Change any input above and every figure here is recalculated in your browser.

Inputs used

Data to cacheminimum 0.001 GB
60 GB
Target hit rateaccepts 1–100 %
95 %
Memory per cache nodeminimum 0.1 GB
26 GB
Replicas per shardaccepts 0–5
1

Results

Cache nodes required
6
Shards
3
Memory needed for the target hit rate
57.0 GB
Usable memory per node
19.5 GB

Step by step

  1. 1Values used
  2. 2Cache sizing
  3. 3Cache nodes required= 6
  4. 4Shards= 3
  5. 5Memory needed for the target hit rate= 57.0 GB
  6. 6Usable memory per node= 19.5 GB

Assumptions and limits

  • The result is derived only from the 4 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 1 decimal place, 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

Why only 75 percent usable?

Redis needs room for the replication backlog, copy-on-write during background saves, and allocator fragmentation. Filling it causes eviction storms or OOM.

Do replicas increase cache capacity?

No, they hold identical data for availability and read scaling. Adding capacity requires more shards, not more replicas.

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