SLA uptime calculator

Enter any availability target and see exactly how much downtime that allows per year, month, week, day, and hour.

Common SLA targets

Allowed downtime

99.9%

Reference table

SLA	Nines	Per year	Per month	Per week

What an SLA percentage actually promises

"99.9% uptime" and "99.99% uptime" sound almost identical, but the allowed downtime behind them differs by an order of magnitude — roughly 8.7 hours per year at three nines, down to about 52 minutes per year at four nines. Each additional nine cuts the allowed downtime by roughly 10x, which is exactly why it gets dramatically harder (and more expensive in redundant infrastructure) to earn each one.

Why this number matters when negotiating a contract

Vendors quote SLA percentages as a marketing figure, but the number that actually matters is the downtime it translates to at your specific scale — 99.9% on a service you depend on every business hour is a very different commitment than 99.9% on something used occasionally. Converting the percentage into hours/minutes per year, month, and week (what this calculator does) turns a marketing number into a concrete, comparable commitment before you sign anything.

What's the real-world difference between 99.9% and 99.99% uptime?

About 8.7 hours of allowed annual downtime at 99.9% (“three nines”), versus about 52 minutes at 99.99% (“four nines”) — roughly a 10x difference in allowed downtime for what looks like a small percentage change. This is why SLA negotiations focus heavily on which specific nine you're being promised.

Why does each additional “nine” get so much more expensive to deliver?

Because the allowed downtime shrinks by roughly 10x with each nine, which generally requires proportionally more redundant infrastructure, faster failover, and tighter operational discipline to actually achieve reliably — the cost of infrastructure to hit each successive nine grows much faster than the percentage number suggests.

Does SLA uptime include planned maintenance windows?

It depends entirely on the specific contract — some SLAs explicitly exclude scheduled maintenance from the downtime calculation, others count it against the total. Always check the actual SLA document's definition of “downtime,” since this varies significantly between vendors and isn't standardized.

Related tools

Infrastructure

Server & Homelab Power Cost Calculator

Add up your server, rack, and homelab gear, set your electricity rate, and see the real daily, monthly, and yearly cost of running it 24/7.

Open →

Infrastructure

Rack Unit & Weight Planner

Plan a rack layout — track U space used, total weight against rack load rating, and catch mixed front-to-back/side-to-side airflow before it becomes a heat problem.

Open →

Infrastructure

Data Size Converter

Convert between bits, bytes, KB, MB, GB, TB, PB and their binary equivalents (KiB, MiB, GiB). Instant browser-side conversion with common size presets.

Open →

Infrastructure

Network Speed Converter

Convert between Mbps, Gbps, MB/s, GB/s and all common network and storage throughput units. Common interface presets for USB, Ethernet, Wi-Fi, NVMe, and more.

Open →

Infrastructure

Network Transfer Time Calculator

Enter a file size and link speed to see how long a transfer will take. Includes real-world estimates for wired and Wi-Fi connections.

Open →

Infrastructure

UPS Runtime Calculator

Enter your UPS battery capacity and connected load to see estimated runtime. Pick from common UPS models and devices for instant results.

Open →

All calculations run locally