Subnet Calculator

Calculate network and broadcast addresses, usable host range, subnet mask, wildcard mask and host count for any IPv4 or IPv6 CIDR block.

Try: 192.168.1.10/24, 10.0.0.0/8, 172.16.5.4/20, 2001:db8:abcd::/48

181.148.0.0/17

IPv4 · Public
IP address
181.148.0.0
Network address
181.148.0.0
Prefix length
/17
Subnet mask
255.255.128.0
Wildcard mask
0.0.127.255
Broadcast address
181.148.127.255
First usable host
181.148.0.1
Last usable host
181.148.127.254
Total addresses
32,768
Usable hosts
32,766
Class
B
Reverse DNS zone
0.0.148.181.in-addr.arpa
IP in binary
10110101.10010100.00000000.00000000
Mask in binary
11111111.11111111.10000000.00000000

Split into 2 × /18: 181.148.0.0/18, 181.148.64.0/18

Split into 4 × /19: 181.148.0.0/19, 181.148.32.0/19, 181.148.64.0/19, 181.148.96.0/19

How to use the subnet calculator

Enter an IP address with a CIDR prefix such as 192.168.1.10/24, or an address plus a dotted subnet mask such as 10.1.2.3 and 255.255.0.0. The calculator works out the network it belongs to and every value you need to configure routers, firewalls, cloud VPCs and DHCP scopes. IPv6 prefixes like 2001:db8::/48 are supported too.

IPv4 CIDR reference table

CIDRSubnet maskUsable hosts
/8255.0.0.016,777,214
/9255.128.0.08,388,606
/10255.192.0.04,194,302
/11255.224.0.02,097,150
/12255.240.0.01,048,574
/13255.248.0.0524,286
/14255.252.0.0262,142
/15255.254.0.0131,070
/16255.255.0.065,534
/17255.255.128.032,766
/18255.255.192.016,382
/19255.255.224.08,190
/20255.255.240.04,094
/21255.255.248.02,046
/22255.255.252.01,022
/23255.255.254.0510
/24255.255.255.0254
/25255.255.255.128126
/26255.255.255.19262
/27255.255.255.22430
/28255.255.255.24014
/29255.255.255.2486
/30255.255.255.2522
/31255.255.255.2542
/32255.255.255.2551

Key terms explained

  • Network address: the first address in the block, which identifies the subnet itself.
  • Broadcast address: the last address in an IPv4 block, used to reach every host on the subnet. IPv6 has no broadcast and uses multicast instead.
  • Usable hosts: total addresses minus the network and broadcast addresses. A /24 has 256 addresses and 254 usable hosts. Point-to-point /31 links (RFC 3021) use both addresses, and a /32 is a single host.
  • Wildcard mask: the inverse of the subnet mask, used in Cisco ACLs and OSPF statements.

Want the full explanation with worked examples? Read Subnet masks and CIDR notation made simple.

Frequently asked questions

What subnet size should I use for my home or office?

A /24 (254 hosts) suits almost any home or small office. Larger networks are usually split into several /24s per floor, department or VLAN.

What is the standard IPv6 subnet size?

A /64 for every LAN segment. ISPs typically delegate a /56 or /48 to each customer, giving 256 or 65,536 subnets.

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