Calculator Inputs
Example Data Table
| Scenario | Link | Utilization | Overhead | Loss | Reserve | Devices | Demand Each | Usable Aggregate | Total Demand |
|---|---|---|---|---|---|---|---|---|---|
| Office switch uplink | 1 Gbps full duplex | 75% | 8% | 1% | 10% | 24 | 18 Mbps | 1.23 Gbps | 432 Mbps |
| Lab imaging network | 10 Gbps full duplex | 70% | 6% | 0.5% | 15% | 40 | 95 Mbps | 11.13 Gbps | 3.80 Gbps |
| Legacy half duplex segment | 100 Mbps half duplex | 60% | 12% | 4% | 10% | 8 | 7 Mbps | 45.62 Mbps | 56 Mbps |
Formula Used
- Nominal per-direction bandwidth = Link Speed converted to Mbps.
- Nominal aggregate bandwidth = Nominal per-direction bandwidth × Duplex Factor.
- Duplex Factor = 2 for full duplex, 1 for half duplex.
- Planning efficiency = (Utilization ÷ 100) × (1 − Overhead ÷ 100) × (1 − Loss ÷ 100) × (1 − Reserve ÷ 100).
- Usable per-direction bandwidth = Nominal per-direction bandwidth × Planning efficiency.
- Usable aggregate bandwidth = Nominal aggregate bandwidth × Planning efficiency.
- Total demand = Active Devices × Average Device Demand.
- Load percentage = Total Demand ÷ Usable Aggregate Bandwidth × 100.
- Frame-based stream estimate = Frame Size × 8 × Packets Per Second ÷ 1,000,000.
- Transfer time = Transfer Size in bits ÷ Usable Per-Direction bits per second.
- Recommended nominal aggregate = Total Demand ÷ Planning efficiency.
This model helps estimate practical LAN capacity after planning limits, protocol cost, retransmissions, and reserved growth headroom are considered.
How to Use This Calculator
- Enter the LAN port speed and choose Mbps, Gbps, or Tbps.
- Select full duplex for modern switched Ethernet links.
- Set a utilization target that matches your planning policy.
- Add protocol overhead to reflect real frame and packet headers.
- Enter retransmission loss if collisions, interference, or retries exist.
- Reserve headroom for bursts, failover traffic, and future growth.
- Provide active device count and average demand per device.
- Enter frame size and packets per second to estimate packet-based traffic.
- Add a transfer size to estimate the duration of one-way file movement.
- Submit the form and review capacity, demand, risk level, and upgrade guidance.
FAQs
1. What does usable bandwidth mean?
Usable bandwidth is the realistic capacity left after utilization policy, protocol headers, retransmissions, and reserved headroom reduce nominal link speed.
2. Why is full duplex treated differently?
Full duplex supports simultaneous send and receive paths. That doubles aggregate bidirectional capacity compared with half duplex, although one-way file transfers still use one direction.
3. Should I set utilization to 100 percent?
Usually no. Running links near saturation increases latency, queue growth, and jitter. Planning at 60 to 80 percent is often safer.
4. What counts as protocol overhead?
Protocol overhead includes Ethernet framing, VLAN tags, IP headers, TCP or UDP headers, acknowledgments, and other non-payload traffic.
5. Why include reserve headroom?
Reserve headroom keeps spare bandwidth for backups, bursts, failover events, onboarding, and seasonal usage growth. It improves resilience.
6. Can this calculator size switch uplinks?
Yes. It is useful for access-to-distribution uplinks, storage paths, office networks, lab segments, and other local Ethernet planning tasks.
7. What does the frame-based stream estimate show?
It converts average frame size and packets per second into Mbps. That helps compare packet-driven traffic with device-demand estimates.
8. How should I read the suggested port class?
It maps the recommended nominal requirement to the next common Ethernet speed class. Use it as upgrade guidance, not a strict rule.