Routing Table Size Calculator
Estimate the memory footprint of a router's routing table (RIB/FIB) from the number of routes and per-route memory cost.
Inputs
Full IPv4 internet routing table is currently roughly 900,000+ routes.
Typical IPv4 RIB entry: ~60-80 bytes depending on platform and attributes stored.
Some platforms store multiple copies (e.g. per line card in a distributed router).
Total Memory Required
60.08MB
Total Memory Required
0.0587GB
Memory per FIB Copy
60.08MB
Total Memory
63,000,000bytes
Step by step
Values used
Number of Routes = 900,000; Average Bytes per Route = 70 bytes; Redundancy / FIB Copies = 1
Routing table memory
memory = routes × avg_bytes_per_route × redundancy_factor
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
How it works
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
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.