Routing Table Size
Estimate memory and entry requirements for a routing table given prefix counts.
About Routing Table Size
Each entry in a router's Routing Information Base (RIB) or Forwarding Information Base (FIB) consumes a roughly fixed amount of memory to store the prefix, next-hop, metric, and associated attributes — commonly estimated at 60-80 bytes per IPv4 route depending on the platform and how much metadata is retained. Total memory demand is simply the number of routes multiplied by that per-route cost, and multiplied again by any redundancy factor for platforms that replicate the FIB across multiple forwarding engines or line cards. This is a key capacity-planning concern for internet-facing routers as the global IPv4 and IPv6 routing tables continue to grow.
Formula
Routing table memory
memory = routes × avg_bytes_per_route × redundancy_factor
- n
- Number of routes
- b
- Average bytes per route
- k
- Number of FIB/RIB copies stored
Worked example
With the default values below, Routing Table Size returns Total Memory Required of 60.08. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Number of Routesminimum 1
- 900,000
- Average Bytes per Routeminimum 1 bytes
- 70 bytes
- Redundancy / FIB Copiesaccepts 1–8
- 1
Results
- Total Memory Required
- 60.08 MB
- Total Memory Required
- 0.0587 GB
- Memory per FIB Copy
- 60.08 MB
- Total Memory
- 63,000,000 bytes
Step by step
- 1Values used
- 2Routing table memory
- 3Total Memory Required= 60.08 MB
- 4Total Memory Required= 0.0587 GB
- 5Memory per FIB Copy= 60.08 MB
- 6Total Memory= 63,000,000 bytes
Assumptions and limits
- The result is derived only from the 3 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 4 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 big is the global IPv4 routing table today?
The full internet default-free zone (DFZ) IPv4 routing table has grown past 900,000-1,000,000 routes and continues increasing over time, which is why older routers with limited TCAM/memory eventually need hardware upgrades or filtering policies to keep operating on the public internet.
Why do routes take up more memory than just the prefix bits?
Each RIB/FIB entry stores far more than the raw prefix: the next-hop address, outgoing interface, metric/cost, administrative distance, BGP attributes (AS path, communities, local preference) for BGP routes, and internal data structure overhead for the tree/trie used for fast lookups — all of which adds up to tens of bytes per entry beyond the prefix itself.
Why would a router need multiple copies of the FIB?
Distributed router architectures with multiple line cards or forwarding engines often replicate the FIB to each one so that every card can make independent, high-speed forwarding decisions without querying a central control plane for every packet — this improves forwarding performance at the cost of multiplying the total memory required across the chassis.