When to use: Use to determine the required WAN/internet circuit bandwidth from user count and application profile. Factors in concurrency (peak simultaneous users), overhead for protocol/retransmission, and target utilization ceiling. Recommended utilization is 70–80% to maintain headroom for bursts. Size to next standard carrier circuit above the required value.
This calculator determines the required WAN or internet circuit bandwidth from user count and application profile. Network engineers use it during site assessments and WAN procurement to select the correct carrier circuit tier before deployment.
The base demand is calculated as Users × Per-User Mbps × Concurrency Factor, where concurrency accounts for the percentage of users simultaneously active at peak. Protocol and retransmission overhead (typically 15%) is then added to the base demand. The required bandwidth is finally de-rated by a maximum utilization ceiling (recommended 70–80%) to maintain headroom for bursts, yielding the minimum circuit size required.
The result is rounded up to the next standard carrier circuit (10, 20, 50, 100, 200 Mbps, etc.). Sizing exactly to predicted demand without headroom results in chronic congestion because TCP traffic is highly bursty and link utilization above 85% degrades application performance significantly.
WAN sizing is governed by vendor best practices rather than a single prescriptive standard. Cisco's Enterprise WAN Design Guide recommends a maximum steady-state utilization of 70–80% to maintain QoS performance and avoid tail-drop packet loss. TIA-942 provides data center network tiering guidelines that inform uplink redundancy and capacity ratios. For access-layer oversubscription, TIA recommends 20:1 at the access tier and 4:1 at distribution. SD-WAN deployments (per IETF RFC standards) add dynamic path selection that can allow higher utilization across bonded circuits.
Application profile mix is critical: a site heavy on video conferencing (4 Mbps/user) requires far more capacity than a call center (1 Mbps/user). Always include a three-year growth margin of 30–50% beyond the immediate requirement. For multi-site organizations, consider SD-WAN with active-active bonding across two circuits so no single ISP failure drops connectivity. WAN QoS policy should mark voice (DSCP EF) and video (DSCP AF4x) at the LAN egress point to ensure priority delivery across the WAN link.
Enter total users, select the application profile that best matches your site's workload, and set the peak concurrency percentage (typically 60–70% for standard offices). Adjust the maximum utilization target and protocol overhead if your environment differs from defaults. The calculator outputs the recommended circuit size alongside the utilization at design load — verify this is below 80%. Use the result to specify a carrier Ethernet, MPLS, or broadband circuit during procurement.
Use 65–70% for a general office. Not all users generate peak traffic simultaneously; typical enterprise measurements show 60–75% concurrent activity during business hours.
TCP congestion control and application retries cause bursty traffic patterns. Sustained utilization above 80–85% causes queue buildup, tail-drop packet loss, and degraded voice and video quality. Industry practice targets 70–80% maximum utilization.
SD-WAN with active-active bonding allows you to sum circuit capacities, so two 100 Mbps circuits provide roughly 200 Mbps aggregate. Model each circuit separately and apply the 70–80% utilization rule to the total bonded capacity.
Cisco and Microsoft recommend 3–4 Mbps per simultaneous video participant for 1080p streams. A site where 70% of users are in video meetings simultaneously should plan for 4 Mbps/user concurrently active.
Industry standard is 30–50% headroom beyond current calculated demand, representing approximately three years of organic growth at 10–15% per year. Size to the next standard circuit that provides this headroom without purchasing excess capacity.
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