Calculate OSPF Cost
This planner uses a stacked page layout, while the calculator fields below adapt to three columns on large screens, two on tablets, and one on mobile.
Example Data Table
This sample assumes a reference bandwidth of 100000 Mbps and floor-style integer conversion.
| Link | Bandwidth (Mbps) | Formula | OSPF Cost |
|---|---|---|---|
| Core Uplink | 10000 | 100000 / 10000 | 10 |
| Distribution Link | 1000 | 100000 / 1000 | 100 |
| WAN Edge | 200 | 100000 / 200 | 500 |
| Branch Access | 100 | 100000 / 100 | 1000 |
| Total Path Cost | 1610 | ||
Formula Used
Interface Cost
OSPF Cost = Reference Bandwidth / Interface Bandwidth
The calculated value is converted to an integer using the selected rounding mode, then limited so it never falls below the chosen minimum cost.
Manual Override Rule
Final Interface Cost = Manual Override
If a manual cost is entered for a link, that value replaces the computed cost. This models direct interface metric tuning on network devices.
Path Cost
Total Path Cost = Sum of All Active Interface Costs
OSPF prefers the route with the lower total path cost. Equal totals may allow equal-cost multipath, depending on platform settings.
How to Use This Calculator
- Enter a path name to identify the route you are modeling.
- Set the reference bandwidth used by your OSPF design.
- Choose the minimum cost and rounding mode for planning.
- Enable each link that belongs to the route.
- Provide bandwidth for every active link in Mbps.
- Add a manual override only when you want an explicit metric.
- Press the calculate button to show the result above the form.
- Review the summary cards, detailed table, and graph, then export CSV or PDF if needed.
FAQs
1) What is OSPF cost?
OSPF cost is the metric used to compare route choices. Each active interface contributes a cost, and the protocol usually prefers the path with the lowest total value.
2) Why should I change the reference bandwidth?
A low reference bandwidth can make very fast links look identical. Raising it helps distinguish 1G, 10G, 40G, and faster interfaces more accurately in modern networks.
3) Does OSPF cost directly measure latency?
No. Standard OSPF cost is based on configured interface metrics, often derived from bandwidth. Delay, jitter, and packet loss are not directly included unless administrators model them through manual tuning.
4) What happens when I enter a manual override?
The manual override replaces the calculated interface cost for that link. This is helpful when device configuration uses a fixed metric rather than the default bandwidth-based value.
5) Why is the minimum cost usually 1?
OSPF metrics are positive integers. Very fast links can otherwise calculate to values below one, so a minimum of 1 keeps the metric valid and operationally meaningful.
6) Should lower or higher OSPF cost be preferred?
Lower total cost is preferred. A smaller number signals a more attractive path according to the configured OSPF metric design.
7) Can equal path costs share traffic?
Yes. If multiple routes have the same total cost, many platforms can install equal-cost multipath routes and distribute traffic across them, subject to device settings and limits.
8) Why does a fast network still show a high total?
The total reflects the sum of all active interfaces on the route. Several moderate-cost hops can produce a large path total even when some individual links are fast.