Subnet Calculator
Calculate network address, broadcast, host ranges, and binary representations for any IPv4 subnet. Includes CCNA/Network+ practice questions.
Calculator
Practice Questions
CCNA / Network+ exam-style questions. Click an answer to reveal the explanation.
About the Subnet Calculator
The Certsqill Subnet Calculator turns an IPv4 address and subnet mask (or CIDR prefix) into everything you need: the network and broadcast addresses, the range of usable host addresses, the total and usable host counts, and the wildcard mask — with a binary breakdown so you can see exactly how the mask works. It is built for CCNA, CompTIA Network+, and Security+ candidates who need to master subnetting quickly and check their manual calculations.
How to use the Subnet Calculator
- Enter an IP address. Type any IPv4 address, for example 192.168.1.0.
- Choose a mask or CIDR prefix. Enter a subnet mask (e.g. 255.255.255.0) or a CIDR prefix (e.g. /24). The calculator accepts either.
- Read the results. See the network address, broadcast address, first and last usable host, total and usable host counts, and the wildcard mask.
- Check the binary view. Switch to the binary breakdown to see exactly how the prefix splits the network bits from the host bits.
- Test yourself. Open the built-in practice questions to drill subnetting under exam-style conditions.
Frequently asked questions
What is a subnet mask?
A subnet mask marks which bits of an IP address identify the network and which identify the host. For example, 255.255.255.0 (a /24) uses the first 24 bits for the network and the last 8 for hosts. Routers use the mask to decide whether two addresses are on the same subnet.
What does CIDR notation like /24 mean?
CIDR (Classless Inter-Domain Routing) notation writes the mask as a slash followed by the number of network bits. /24 means 24 network bits (255.255.255.0), /16 means 16 (255.255.0.0), and /8 means 8 (255.0.0.0). A larger prefix means a smaller subnet.
How many hosts are in a /24 subnet?
A /24 has 256 total addresses (2^8), but two are reserved — the network address and the broadcast address — leaving 254 usable host addresses.
How do I calculate the number of usable hosts?
Raise 2 to the power of the number of host bits, then subtract 2 for the network and broadcast addresses. Host bits = 32 − CIDR prefix. For a /26 that is 32 − 26 = 6 host bits, so 2^6 − 2 = 62 usable hosts.
What is a wildcard mask?
A wildcard mask is the inverse of a subnet mask — subtract each octet from 255. Cisco access control lists and OSPF use it to match ranges of addresses. For a /24, the subnet mask 255.255.255.0 becomes the wildcard 0.0.0.255.
What is the difference between the network and broadcast address?
The network address is the first address in the subnet (all host bits 0) and names the subnet itself; the broadcast address is the last (all host bits 1) and reaches every host on the subnet. Neither can be assigned to a device.
Master subnetting for Network+ and CCNA with exam-accurate questions and a detailed explanation on every answer — 20 free, no credit card.
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