Docker Bridge Network Calculator
Calculate how many containers a Docker bridge network's subnet can support.
Inputs
CIDR prefix length (e.g. 24 for /24 = 254 usable IPs).
IPs reserved (network, broadcast, gateway = minimum 3).
Number of containers you plan to run on this bridge.
Usable Container IPs
253
IP Headroom
203IPs
Subnet Utilization
19.8%
Total IPs in Subnet
256
Step by step
Total IPs in subnet
2^(32 − 24)
= 256
Usable IPs
256 − 3
= 253
Utilization
50 / 253
= 19.8%
How it works
A Docker bridge network assigns one IP per container from its subnet. Usable IPs = 2^(32−CIDR) − reserved. A /24 gives 254 usable addresses (256 − network − broadcast); a /16 gives ~65,533.
Formula
Usable IPs
usableIPs = 2^(32 − CIDR) − reserved
- CIDR
- Subnet prefix length
- reserved
- Reserved addresses (network, broadcast, gateway)
Frequently Asked Questions
What happens when the subnet runs out of IPs?
Docker will fail to start new containers with an error like 'no available IPs in pool'. You'd need to create additional bridge networks with different subnets.
Can I use multiple bridge networks?
Yes — each user-defined bridge network has its own subnet. Containers can be attached to multiple networks for cross-network communication.
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