Log Storage Retention Calculator
Sizing log storage is a simple volume problem: how much data arrives each day, how long you keep it, and how well it compresses. This calculator converts an events-per-second rate and an average event size into a daily ingest volume, scales that by your retention period, divides by your compression ratio, and multiplies by your replication factor. The result tells you how many gigabytes you must provision so that retention does not silently drop the oldest logs. Compression ratio, retention, and replication are platform and policy dependent, so they are entered as your own values rather than assumed.
Log storage formula
Raw daily bytes = events/sec * avg size * 86,400
GB uses 1 GB = 1,000,000,000 bytes (SI)
Raw total = raw daily * retention days
Stored = raw total / compression ratio
Provisioned = stored * replication factor
Bytes are converted to gigabytes using the SI decimal definition (1 GB = 10^9 bytes), as used by storage vendors. If your platform reports binary gibibytes, divide GB by 1.073741824 to convert.
Capacity planning context
- The seconds-per-day constant is exact at 86,400 (60 * 60 * 24).
- Compression ratio varies widely by log format and platform: enter the ratio your own system reports rather than a generic figure.
- Indexes and metadata add to stored size in many search-based log systems; add headroom for them separately.
- Retention should match your operational and compliance requirements; NIST SP 800-92 discusses log management and retention practice.
- Provision headroom above the calculated figure to absorb traffic spikes and avoid dropping the oldest logs.
Log storage: frequently asked questions
How do I size log storage?
Multiply the daily ingest volume by the number of retention days. Daily ingest equals events per second times average event size times 86,400 seconds per day. Divide by the compression ratio if your platform compresses stored logs. The result is the storage you must provision before any replication or overhead.
What is a typical log compression ratio?
Compression ratio is platform and data dependent, so it ships here as a user-editable input. Plain-text logs commonly compress between 5:1 and 15:1. Enter the ratio your own system reports. A ratio of 1 means no compression. The calculator divides raw volume by this ratio to give stored size.
Does this include replication and indexing overhead?
The base figure is compressed primary storage. Many systems add an index that is a fraction of raw size, plus replica copies. Use the replication factor input to multiply stored size by the number of copies you keep. Add headroom separately for indexes and operating margin.
Why use events per second rather than per day?
Events per second is the unit most logging pipelines and monitoring tools report, so it is easy to read off a dashboard. The calculator converts to a daily figure using 86,400 seconds per day, then scales by retention. You can enter a fractional rate such as 0.5 for low-volume systems.
What retention period should I keep?
Retention is driven by your operational and compliance requirements, not by a fixed rule, so it is a user input. Security and audit logs often require longer retention than debug logs. Confirm the period required by your own policy and any regulation that applies to your data, then enter it here.
Official sources
- NIST: SP 800-92, Guide to Computer Security Log Management.
- NIST: Metric (SI) prefixes for byte unit definitions.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.