Enter an address and a prefix to get the netmask, wildcard mask, broadcast address, usable host range, and host count — then divide the block into the subnets you actually need. Everything is calculated in your browser, and the URL updates so you can share or bookmark a result.
| CIDR block | 192.168.1.0/24 |
|---|---|
| Network address | 192.168.1.0 |
| Netmask | 255.255.255.0 |
| Wildcard mask | 0.0.0.255 |
| Broadcast address | 192.168.1.255 |
| Usable host range | 192.168.1.1 – 192.168.1.254 |
| Usable hosts | 254 |
| Total addresses | 256 |
| Netmask (binary) | 11111111.11111111.11111111.00000000 |
| Netmask (hex) | 0xFFFFFF00 |
| Network (binary) | 11000000.10101000.00000001.00000000 |
| Reverse DNS zone | 1.168.192.in-addr.arpa |
| Legacy class | C |
| Scope | Private (RFC 1918) |
Split any row in half, then keep splitting only the halves you need — a VLAN plan with uneven subnets (a /26 for workstations, a /30 for a router link) falls out of a few clicks. Join puts a pair back together.
| Subnet | Netmask | Host range | Hosts | |
|---|---|---|---|---|
| 192.168.1.0/24 | 255.255.255.0 | 192.168.1.1 – 192.168.1.254 | 254 |
Host counts exclude the network and broadcast addresses, except on /31 (RFC 3021) and /32.
iDRAC, iLO, and IPMI ports belong on a management subnet that is separate from production traffic and not reachable from the internet. A /27 covers 30 controllers, which is a full rack with room left over. Keeping it separate is also what lets you firewall BMC access down to a jump host without touching production rules.
Renumbering a live subnet is the expensive part, not the addresses themselves. If a VLAN holds 40 hosts now, a /25 costs nothing extra and absorbs growth; a /26 sized exactly to today leaves you splitting VLANs later. Take the space from 10.0.0.0/8 and it stays cheap.
Allocate subnets on boundaries you can summarise later — one /16 per site, one /24 per VLAN inside it. Contiguous, aligned blocks collapse into a single route advertisement; blocks handed out first-come-first-served do not, and the routing table grows for the rest of the network’s life.
Working out how many NICs and BMC ports a build needs in the first place? Configure the server and the networking options are priced live alongside the rest of the hardware.
Every prefix from /8 to /32 with its netmask, wildcard mask, address count, and usable hosts. Usable hosts drop the network and broadcast addresses, except at /31 and /32.
| Prefix | Netmask | Wildcard | Addresses | Usable hosts | Classful equivalent |
|---|---|---|---|---|---|
| /8 | 255.0.0.0 | 0.255.255.255 | 16,777,216 | 16,777,214 | 1 class A |
| /9 | 255.128.0.0 | 0.127.255.255 | 8,388,608 | 8,388,606 | 128 class B |
| /10 | 255.192.0.0 | 0.63.255.255 | 4,194,304 | 4,194,302 | 64 class B |
| /11 | 255.224.0.0 | 0.31.255.255 | 2,097,152 | 2,097,150 | 32 class B |
| /12 | 255.240.0.0 | 0.15.255.255 | 1,048,576 | 1,048,574 | 16 class B |
| /13 | 255.248.0.0 | 0.7.255.255 | 524,288 | 524,286 | 8 class B |
| /14 | 255.252.0.0 | 0.3.255.255 | 262,144 | 262,142 | 4 class B |
| /15 | 255.254.0.0 | 0.1.255.255 | 131,072 | 131,070 | 2 class B |
| /16 | 255.255.0.0 | 0.0.255.255 | 65,536 | 65,534 | 1 class B |
| /17 | 255.255.128.0 | 0.0.127.255 | 32,768 | 32,766 | 128 class C |
| /18 | 255.255.192.0 | 0.0.63.255 | 16,384 | 16,382 | 64 class C |
| /19 | 255.255.224.0 | 0.0.31.255 | 8,192 | 8,190 | 32 class C |
| /20 | 255.255.240.0 | 0.0.15.255 | 4,096 | 4,094 | 16 class C |
| /21 | 255.255.248.0 | 0.0.7.255 | 2,048 | 2,046 | 8 class C |
| /22 | 255.255.252.0 | 0.0.3.255 | 1,024 | 1,022 | 4 class C |
| /23 | 255.255.254.0 | 0.0.1.255 | 512 | 510 | 2 class C |
| /24 | 255.255.255.0 | 0.0.0.255 | 256 | 254 | 1 class C |
| /25 | 255.255.255.128 | 0.0.0.127 | 128 | 126 | 1/2 class C |
| /26 | 255.255.255.192 | 0.0.0.63 | 64 | 62 | 1/4 class C |
| /27 | 255.255.255.224 | 0.0.0.31 | 32 | 30 | 1/8 class C |
| /28 | 255.255.255.240 | 0.0.0.15 | 16 | 14 | 1/16 class C |
| /29 | 255.255.255.248 | 0.0.0.7 | 8 | 6 | 1/32 class C |
| /30 | 255.255.255.252 | 0.0.0.3 | 4 | 2 | 1/64 class C |
| /31 | 255.255.255.254 | 0.0.0.1 | 2 | 2 | 1/128 class C |
| /32 | 255.255.255.255 | 0.0.0.0 | 1 | 1 | 1/256 class C |
Take 2 to the power of the number of host bits, then subtract two for the network and broadcast addresses. A /24 has 8 host bits, so 256 addresses and 254 usable hosts; a /26 has 6, so 64 addresses and 62 hosts. The two exceptions are /31, which carries two usable addresses because RFC 3021 removed the network and broadcast pair on point-to-point links, and /32, a single host route.
They are two spellings of the same value. The prefix counts the leading 1 bits — /24 means 24 ones — and the netmask writes those same bits as dotted decimal, 255.255.255.0. Every valid netmask is a contiguous run of ones followed by zeros, which is why 255.255.255.0 is legal and 255.0.255.0 is not.
A wildcard mask is the netmask with every bit inverted, so 255.255.255.0 becomes 0.0.0.255. Cisco IOS access lists, OSPF network statements, and several firewall syntaxes match on it rather than on the netmask — a 1 bit means "ignore this bit". The calculator prints it next to the netmask so you can paste either form.
RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 for private use, and RFC 6598 adds 100.64.0.0/10 for carrier-grade NAT. Pick from 10/8 if you expect to grow — it gives you room to give each site, rack, or VLAN its own /16 without renumbering later.
Each additional prefix bit halves the block: a /24 splits into two /25s, four /26s, eight /27s, and so on. Use the divider above — split the block, then split only the halves that need to be smaller. Subnets do not have to be the same size, which is the point of variable-length subnet masking (VLSM); they only have to start on their own boundary, which the divider enforces for you.
Use a /31 if both ends support it, which nearly all current routing platforms do. A /30 spends four addresses to deliver two usable ones; a /31 delivers the same two out of two. On a large network that is thousands of addresses returned to the pool. Keep /30 only where an older device or a management tool refuses the /31.
No. The math runs in your browser, and the address you calculate appears only in your own URL so the result stays shareable and bookmarkable. Nothing is stored on our side.
Not yet — this tool is IPv4 only. IPv6 subnetting is mostly a different exercise anyway: prefixes land on nibble boundaries, /64 is the standard LAN size regardless of host count, and address exhaustion inside a subnet stops being the constraint you plan around.