Subnet Calculator — IPv4 / IPv6 CIDR
Compute network, mask, wildcard, usable hosts, and address class for IPv4 or IPv6. Fully local.
Developer notes
Address without a slash — “/24” in the address field is an error. Mask mode is IPv4-only. IPv4 /31 = 2 hosts (RFC 3021); /32 = 1. IPv6: usable = total; no L2 broadcast. 64 KiB limit.
Options
- Prefix mode
- cidr = length /24; mask = IPv4 dotted mask (255.255.255.0).
- Show binary
- Adds binary fields for address / network / mask (IPv4).
- Host count style
- usable follows IPv4 rules, and for IPv6 it equals total. total is 2^(host bits).
When teams pick this route
Check an addressing plan before deploy. Compare usable vs total. Show binary view to debug a mask.
Worked examples
IPv4 /24
Before
After
IPv6 /64
Before
After
Related networking tools
Hub networking tools. For numeric base conversion: number-base-converter.
Subnet calculator FAQ
Local IPv4 / IPv6 CIDR
When should I use the number-base converter instead?
To convert an integer between bases 2–36 (hex of a number, binary of a value), use number-base-converter. Networking tools compute subnets and CIDRs, not general base conversion.
Are IP addresses uploaded?
No. All math runs locally in your browser. Nothing is uploaded to FastMinify.
What is the size limit?
64 KiB (UTF-8) for the combined input fields of each tool.
Why is there no IPv6 broadcast?
IPv6 has no L2 broadcast like IPv4. The tool shows the network prefix and the last address in the block; usable equals total.
Networking / IP
CIDR, subnets, and IPv4/IPv6 helpers — in your browser.
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