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RADIUS Capacity Calculator

Size RADIUS servers from authentication rate, interim accounting load and peak-to-average factor.

About RADIUS Capacity Calculator

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

Worked example

With the default values below, RADIUS Capacity Calculator returns Total Transactions Per Second of 18.89. Change any input above and every figure here is recalculated in your browser.

Inputs used

Users or devicesminimum 1 users
20,000 users
Authentications per user per dayminimum 0.1 auths/day
6 auths/day
Peak-to-average factoraccepts 1–30 ×
4 ×
Concurrent accounted sessionsminimum 0 sessions
12,000 sessions
Interim accounting intervalminimum 1 min
15 min
Capacity per serverminimum 1 tps
500 tps

Results

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

Step by step

  1. 1Values used
  2. 2RADIUS Capacity
  3. 3Combined server load
  4. 4Total Transactions Per Second= 18.89 tps
  5. 5Peak Authentication Rate= 5.56 auths/s
  6. 6Interim Accounting Rate= 13.33 records/s
  7. 7Average Authentication Rate= 1.389 auths/s
  8. 8Servers Required (N+1)= 2

Assumptions and limits

  • The result is derived only from the 6 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 3 decimal places, 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

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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