How the calculation works
The calculator adds up traffic at the busiest time of day, separately for download and upload:
- General use = active users × per-user rate. Active users = people on site × the share online at the busiest time, rounded up to a whole person.
- Voice = calls at once × 100 kbps each way.
- Video = devices in video meetings at once × the per-device rate. A laptop, phone or conference-room system counts once, however many people sit in front of it.
- Guest Wi-Fi = the cap you set for the guest network, counted in both directions.
- Large transfers = the Mbps you set aside for big uploads or downloads at peak.
- Cloud backup = data per backup × 8,000 ÷ (window in hours × 3,600), in Mbps, upload only. A backup during business hours adds to the peak. A backup outside business hours doesn’t, but the upload must still be fast enough to finish in the window, so the upload need is the higher of the two.
Recommended = peak × (1 + headroom). For a symmetric circuit such as dedicated internet access (DIA), the size is the higher of the download and upload figures, rounded up to the next common speed tier (10, 20, 25, 50, 75, 100, 200, 250, 300 or 500 Mbps, or 1, 2, 2.5, 5 or 10 Gbps). Tiers vary by provider and location.
Sources and assumptions:
- Voice: a G.711 call with 20 ms packets is 87.2 kbps each way on Ethernet (Cisco): 160 bytes of voice, 40 bytes of IP/UDP/RTP and 18 bytes of Ethernet header, 50 times a second. The calculator rounds it up to 100 kbps for encryption and VPN overhead.
- Video presets: Microsoft’s Teams network guidance for meetings, per device (recommended 2,500 kbps up / 4,000 down; best performance 4,000 / 4,000), and Zoom’s bandwidth requirements for group video (720p: 2.6 Mbps up / 1.8 down; 1080p: 3.8 up / 3.0 down), as published in October 2026. Both apps lower quality when bandwidth is short.
- Planning assumptions with no published source: the per-user rates for light (1 / 0.25 Mbps), typical (2 / 0.5 Mbps) and heavy (5 / 2 Mbps) work, 80% of people online at the busiest time, and 30% headroom. Replace them with figures from your own usage graphs where you can.
Worked example
A 50-person office with the typical profile, 80% online at the busiest time, 10 calls and 8 devices in video meetings at once (Teams recommended rates), a 10 Mbps guest Wi-Fi cap and a 200 GB nightly backup in an 8-hour window:
| Traffic | Download | Upload |
|---|---|---|
| General use: 40 active users × 2 / 0.5 Mbps | 80 Mbps | 20 Mbps |
| Voice: 10 calls × 0.1 Mbps | 1 Mbps | 1 Mbps |
| Video: 8 devices × 4 / 2.5 Mbps | 32 Mbps | 20 Mbps |
| Guest Wi-Fi cap | 10 Mbps | 10 Mbps |
| Peak demand | 123 Mbps | 51 Mbps |
The backup needs 200 × 8,000 ÷ (8 × 3,600) = 55.56 Mbps of upload overnight, more than the daytime peak, so it sets the upload need. With 30% headroom:
- Download: 123 × 1.3 = 159.9 Mbps
- Upload: 55.56 × 1.3 = 72.2 Mbps
- Symmetric circuit: 159.9 Mbps, so the next common tier is 200 Mbps
- A failover link should carry at least (1 + 32) × 1.3 = 42.9 Mbps down and (1 + 20) × 1.3 = 27.3 Mbps up for voice and video, plus the applications that must keep working.
If the same backup ran during business hours it would add 55.56 Mbps to the 51 Mbps peak: 106.6 Mbps of upload, or 138.5 Mbps with headroom.
Redundancy
A single circuit is a single point of failure: a cut fiber, a failed router or a provider outage takes the whole office offline. What to add depends on what an outage costs you:
- Second wired circuit from a different provider, ideally entering the building on a different path, for offices where downtime stops the business. Ask both providers for route diversity details; two circuits in the same conduit can fail together.
- SD-WAN in front of two links fails over automatically, can steer calls and meetings to the better link, and lets you use both links day to day instead of paying for one that sits idle.
- Fixed wireless or an LTE or 5G router as a lower-cost backup where a second wired provider isn’t available. Check its upload against the failover figure above; cellular plans may also have data caps.
The uptime SLA calculator shows how two independent links combine into higher availability than either one alone.
