P95 utilization
Last updated 2026-06-04
P95 utilization is the 95th percentile of a resource's usage measured over a period: the level that actual usage stays at or below 95 percent of the time. It is widely used in rightsizing because it captures typical peak demand while ignoring the rare, brief spikes that would otherwise force permanent over-provisioning. To compute it, observed samples (CPU, memory, network throughput, or IOPS) are collected at a fixed interval, sorted, and the value at the 95th-percentile rank is read off, so only the busiest moments sit above it. Sizing a resource to its P95, plus a safety margin, preserves performance headroom while removing the waste of provisioning for the absolute maximum. Averages, by contrast, can mask real peaks and lead to under-sizing, since a low mean may still hide sustained high-demand windows. Choosing P95 over the raw maximum is what lets rightsizing cut cost without risking saturation. LevelFour bases its rightsizing recommendations on percentile usage such as P95, so they protect performance while reducing cost.
Frequently asked questions
- Why use P95 utilization instead of average or maximum?
- The average can hide real demand peaks and lead to under-sizing, while the absolute maximum reflects rare, brief spikes and forces permanent over-provisioning. P95 sits between them, capturing typical peak demand and ignoring the busiest 5 percent of moments, which balances performance headroom against cost.
- How is P95 utilization calculated?
- Usage samples for a metric (such as CPU, memory, network throughput, or IOPS) are collected at a fixed interval over a chosen window, then sorted. The value at the 95th-percentile rank is the P95: the level usage stays at or below 95 percent of the time, with only the busiest 5 percent of samples above it.
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