SD-WAN Link Calculator

Size the SD-WAN circuit for a branch from user count, concurrency, growth and overlay overhead.

About SD-WAN Link Calculator

The busy-hour rate is applied only to concurrent users, then inflated for growth over the contract term and for tunnel encapsulation. Rounding up to a carrier tier turns the figure into something you can actually order. Branch circuits are contracted for two or three years, so a 20% sizing error is either a permanent overspend or a permanent congestion ticket queue.

Formula

SD-WAN Link

required = users × concurrency × per-user rate × (1 + growth) × (1 + overlay overhead), rounded up to the next carrier tier.

concurrency: Fraction of the population active in the busy hour
overlay overhead: Extra bytes from IPsec, GRE or VXLAN on the SD-WAN fabric

Worked example

With the default values below, SD-WAN Link Calculator returns Bandwidth Required of 29.16. Change any input above and every figure here is recalculated in your browser.

Inputs used

Users at the siteaccepts 1–20,000 users: 120 users
Busy-hour rate per useraccepts 16–50,000 kbps: 400 kbps
Concurrent usersaccepts 1–100 %: 45 %
Growth allowanceaccepts 0–200 %: 25 %
Overlay and tunnel overheadaccepts 0–40 %: 8 %

Results

Bandwidth Required: 29.16 Mbps
Recommended Circuit Tier: 50 Mbps
Utilisation at That Tier: 58.3%
Concurrent Users: 54
Order This Service: 50 Mbps circuit

Step by step

1Values used
2SD-WAN Link
3Bandwidth Required= 29.16 Mbps
4Recommended Circuit Tier= 50 Mbps
5Utilisation at That Tier= 58.3
6Concurrent Users= 54
7Order This Service= 50 Mbps circuit

Assumptions and limits

The result is derived only from the 5 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 2 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 SD-WAN Link calculated?

required = users × concurrency × per-user rate × (1 + growth) × (1 + overlay overhead), rounded up to the next carrier tier. The busy-hour rate is applied only to concurrent users, then inflated for growth over the contract term and for tunnel encapsulation. Rounding up to a carrier tier turns the figure into something you can actually order.

Why does SD-WAN Link matter?

Branch circuits are contracted for two or three years, so a 20% sizing error is either a permanent overspend or a permanent congestion ticket queue.

What values do I need to enter?

This calculator takes 5 inputs: Users at the site, Busy-hour rate per user, Concurrent users, Growth allowance, Overlay and tunnel overhead. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.