Subnet Calculator
Compute network address, broadcast, mask, wildcard, host range, and counts for any IPv4 CIDR block.
What is Subnet Calculator?
A subnet calculator takes an IPv4 CIDR block (for example 192.168.1.0/24) and derives the full set of addresses that block defines: the network address (host bits all zero), the broadcast address (host bits all one), the subnet mask and its bitwise inverse (the wildcard mask used in ACLs), the range of assignable host addresses, and the total and usable host counts. CIDR notation packs a prefix length into the address itself, replacing the older classful A/B/C scheme and letting a single octet boundary be split into many smaller networks. This tool also reports the historical classful class of the first octet and flags RFC 1918 and CGNAT private ranges, which are useful when planning an internal network that should never appear on the public internet.
How to Use Subnet Calculator
- Type a CIDR block such as 192.168.1.0/24 (a bare address like 10.0.0.5 is treated as /32).
- Click "Calculate" or press Enter to compute the subnet breakdown.
- Read off the network address, broadcast, mask, wildcard, host range, and counts from the results table.
- Tap the copy button next to any value to copy just that field.
Examples
Typical home LAN
Input: 192.168.1.0/24
Output: Network 192.168.1.0 · broadcast 192.168.1.255 · mask 255.255.255.0 · 254 usable hosts · class C
Point-to-point link
Input: 10.0.0.0/30
Output: Network 10.0.0.0 · broadcast 10.0.0.3 · usable hosts 10.0.0.1 – 10.0.0.2 · 2 usable hosts
Common Mistakes
- Confusing the network address with the first usable host address — on a /24 the network is .0, but the first assignable host is .1.
- Specifying host bits in the CIDR (e.g. 192.168.1.55/24) and expecting them to be honored — the tool reports the network those bits fall inside; only the prefix bits determine the subnet.
- Forgetting that /31 and /32 are special cases: /31 has no separate network/broadcast, and /32 represents a single host, not a range.
- Treating private RFC 1918 ranges as if they were routable on the public internet — they must be NATted or otherwise translated to reach outside networks.
Why Use This Tool
- Bit-exact 32-bit math using BigInt, so host counts and masks are correct even for /0 and other wide blocks.
- Reports every commonly-needed value (network, broadcast, mask, wildcard, host range, counts) in one table with per-field copy buttons.
- Flags private-use ranges automatically, helping catch configuration mistakes that would break internet routing.
- Fully client-side — no network calls, no data leaving the browser, instant results.