CIDR Calculator
Turn a CIDR block into a human-readable subnet: network address, broadcast, first/last host, total addresses, and usable hosts.
Quick answer: Turn a CIDR block into a human-readable subnet: network address, broadcast, first/last host, total addresses, and usable hosts.
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Frequently asked questions
- What does /24 mean in CIDR?
- /24 means the first 24 bits identify the network, leaving 8 bits for hosts. That's 256 total addresses or 254 usable hosts (network + broadcast are reserved).
- How many IPs are in a /26?
- 64 total, 62 usable — 2^(32-26) = 64 addresses minus the network and broadcast addresses.
- What's the difference between subnet mask and CIDR?
- They express the same thing two ways: 255.255.255.0 = /24. CIDR is shorter and is what modern routing tables use.
- How do I calculate the network and broadcast addresses?
- Network = IP AND mask. Broadcast = network OR (NOT mask). The calculator does this for you instantly.
- What is a private IP range?
- RFC 1918 reserves 10/8, 172.16/12, and 192.168/16 for private use. They're never routed on the public internet, which is why home networks all use them.
- What's the difference between /32 and /0?
- /32 is a single host. /0 covers the entire IPv4 space (0.0.0.0/0). /0 is the default route on every internet-facing router.
- How do I split a network into subnets?
- Take a larger block (e.g. /16) and increase the prefix length to carve out smaller pieces. Each extra bit doubles the number of subnets and halves their size.
- What is VLSM?
- Variable Length Subnet Masking — different subnets in the same network can have different prefix lengths. It lets you give big subnets to busy LANs and small ones to point-to-point links.
- Does this work for IPv6?
- Not yet — this calculator is IPv4-only. IPv6 subnets are usually /64 by convention and don't need the same broadcast/host math.
- Can I calculate multiple subnets at once?
- Right now it's one CIDR per session. Use the IPv4 Subnet Calculator if you want to plan a network from a host count instead of a CIDR.