Docker Bridge Network Calculator

Calculate how many containers a Docker bridge network's subnet can support.

About Docker Bridge Network Calculator

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)

Worked example

With the default values below, Docker Bridge Network Calculator returns Usable Container IPs of 253. Change any input above and every figure here is recalculated in your browser.

Inputs used

Subnet CIDR Prefixaccepts 16–30 /bits: 24 /bits
Reserved IPsaccepts 2–100 IPs: 3 IPs
Containers Neededaccepts 1–1,000,000 containers: 50 containers

Results

Usable Container IPs: 253
IP Headroom: 203 IPs
Subnet Utilization: 19.8%
Total IPs in Subnet: 256

Step by step

1Total IPs in subnet= 256
2Usable IPs= 253
3Utilization= 19.8%

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 1 decimal place, 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

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.