Subnet Calculator — IPv4 / IPv6 CIDR

Compute network, mask, wildcard, usable hosts, and address class for IPv4 or IPv6. Fully local.

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Subnet calculator
Two fields: IP address (no /) and prefix (length or IPv4 mask). Shows network, hosts, and class — not cloud reserved ranges.

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 (IPv4 rules; IPv6 equals total) or total = 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

192.0.2.10

After

network 192.0.2.0 · broadcast 192.0.2.255 · usable 254

IPv6 /64

Before

2001:db8::1

After

network 2001:db8:: · last address in /64 · no L2 broadcast

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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