RADIUS Capacity Calculator
Size RADIUS servers from authentication rate, interim accounting load and peak-to-average factor.
Inputs
Total Transactions Per Second
18.89tps
Peak Authentication Rate
5.56auths/s
Interim Accounting Rate
13.33records/s
Average Authentication Rate
1.389auths/s
Servers Required (N+1)
2
Step by step
Values used
Users or devices = 20,000 users; Authentications per user per day = 6 auths/day; Peak-to-average factor = 4 ×; Concurrent accounted sessions = 12,000 sessions; Interim accounting interval = 15 min; Capacity per server = 500 tps
RADIUS Capacity
peak auth rate = users × auths per day ÷ 86400 × peak factor; interim accounting rate = concurrent sessions ÷ interim interval.
Combined server load
total tps = peak authentications + interim accounting records
Total Transactions Per Second
= 18.89 tps
Peak Authentication Rate
= 5.56 auths/s
Interim Accounting Rate
= 13.33 records/s
Average Authentication Rate
= 1.389 auths/s
Servers Required (N+1)
= 2
How it works
RADIUS load has two independent components: authentication, which spikes at shift changes and after an outage, and interim accounting, which is a steady drip proportional to concurrent sessions. Both hit the same server, so capacity is sized on their sum with a spare unit for redundancy. Wireless 802.1X re-authentication and roaming can push the peak factor above ten, and a RADIUS server that queues under a login storm locks every user off the network at once.
Formulas
RADIUS Capacity
peak auth rate = users × auths per day ÷ 86400 × peak factor; interim accounting rate = concurrent sessions ÷ interim interval.
- auths per day
- Re-authentications per user, driven by session timeout and roaming
- peak factor
- Morning login storm relative to the daily average
- interim interval
- Seconds between Interim-Update accounting records
Combined server load
total tps = peak authentications + interim accounting records
- concurrent sessions
- Sessions being accounted at any instant
Frequently Asked Questions
How is RADIUS Capacity calculated?
peak auth rate = users × auths per day ÷ 86400 × peak factor; interim accounting rate = concurrent sessions ÷ interim interval. RADIUS load has two independent components: authentication, which spikes at shift changes and after an outage, and interim accounting, which is a steady drip proportional to concurrent sessions. Both hit the same server, so capacity is sized on their sum with a spare unit for redundancy.
Why does RADIUS Capacity matter?
Wireless 802.1X re-authentication and roaming can push the peak factor above ten, and a RADIUS server that queues under a login storm locks every user off the network at once.
What values do I need to enter?
This calculator takes 6 inputs: Users or devices, Authentications per user per day, Peak-to-average factor, Concurrent accounted sessions, Interim accounting interval, Capacity per server. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
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