What is it?
The IP Subnet Calculator shows the network address, broadcast address, subnet mask, wildcard mask, first and last usable host, and number of hosts for an IPv4 subnet.
Who is it for?
Network admins, IT support staff, students preparing for CCNA and networking exams, and anyone setting static IPs on home or office devices.
How to use it
Write an address and prefix, like 192.168.1.10/24 or 10.0.0.5 255.255.255.0. The prefix goes from /0 to /32.
Quick reference
- /24 (255.255.255.0): 256 addresses, 254 usable hosts. A typical home network.
- /30: 4 addresses, 2 hosts, for point-to-point links. /31 and /32 are special cases.
- Each step smaller in prefix doubles the size: /23 = 512 addresses.
Private ranges
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are private: used inside homes and offices, not on the internet. 100.64.0.0/10 is used by some internet providers (CGNAT).
Uses
- Setting a static IP on a router, printer or CCTV recorder within the right range.
- Firewall and cloud security-group rules (the wildcard mask is used in Cisco ACLs).
- Networking exam practice (CCNA).
IPv6 isn’t covered.
Worked example
192.168.1.10/24 gives: network 192.168.1.0, broadcast 192.168.1.255, mask 255.255.255.0, wildcard 0.0.0.255, usable hosts 192.168.1.1 to 192.168.1.254 (254 hosts).
10.0.5.70/26 gives: network 10.0.5.64, broadcast 10.0.5.127, hosts .65 to .126 (62 hosts).
Home and office tips
- Keep static addresses (printers, CCTV, NAS) outside the router’s DHCP range so two devices never get the same address. If DHCP gives out .100–.199, use .10–.50 for static devices.
- Two networks that overlap (for example both 192.168.1.0/24 at home and on the office VPN) cause connection problems; change one router to 192.168.2.0/24.
Exam tip
Hosts per subnet = 2^(32 − prefix) − 2. For /27: 2⁵ − 2 = 30 hosts. Block size = 256 − the last mask number (for /27, 256 − 224 = 32), so networks start at .0, .32, .64…
Errors and how to fix them
- Write an address and prefix…: the input isn’t in the form 192.168.1.10/24 or address plus mask.
- “The prefix goes from /0 to /32”: use a prefix in that range.
- Invalid address: each part must be 0–255.
Open the tool: IP Subnet Calculator
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Questions, or an error not listed here?
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