Reference
Common Subnet Sizes (CIDR Quick Reference)
| Prefix | Subnet mask | Total IPs | Usable hosts | Common use |
|---|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 | Class A — large ISP / enterprise |
| /16 | 255.255.0.0 | 65,536 | 65,534 | Class B — campus / large office |
| /24 | 255.255.255.0 | 256 | 254 | Class C — standard office LAN |
| /25 | 255.255.255.128 | 128 | 126 | Split /24 into two halves |
| /26 | 255.255.255.192 | 64 | 62 | Small office / VLAN segment |
| /27 | 255.255.255.224 | 32 | 30 | Small team network |
| /28 | 255.255.255.240 | 16 | 14 | Small cloud subnet |
| /29 | 255.255.255.248 | 8 | 6 | Very small segment |
| /30 | 255.255.255.252 | 4 | 2 | Point-to-point link |
| /32 | 255.255.255.255 | 1 | 0 | Single host / loopback route |
Reference
Private IP Address Ranges (RFC 1918)
10.0.0.0/8
10.0.0.0 – 10.255.255.255
16.7 million addresses
Large enterprise networks, data centers
172.16.0.0/12
172.16.0.0 – 172.31.255.255
1.05 million addresses
Medium networks, Docker default bridge
192.168.0.0/16
192.168.0.0 – 192.168.255.255
65,536 addresses
Home routers, small office LANs
Private IP ranges are not routable on the public internet. Routers use NAT (Network Address Translation) to map private IPs to a public IP for internet access. IPv6 uses fc00::/7 for its private (ULA) address range.
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Tool guide
How to read CIDR and subnet calculator results
Use the CIDR calculator to turn an IP address and prefix into network address, broadcast address, subnet mask, wildcard mask, usable host range, and total address count.
Recommended workflow
- Enter the IPv4 address with CIDR prefix, such as 192.168.1.0/24 or 10.10.10.0/28.
- Check the network address and broadcast address before assigning devices, firewall rules, or static routes.
- Use the first and last usable host values to avoid accidentally using reserved network or broadcast addresses.
Before relying on the result
- Verify whether your network uses /31 or /32 behavior before applying host counts to point-to-point or single-host routes.
- Confirm subnet changes against router, DHCP, VLAN, and firewall configuration before deploying to production.
- Document the CIDR prefix and subnet mask together so other administrators can read the address plan clearly.
Help & answers
Frequently Asked Questions
Important disclaimer: Alexonic Tools is completely free to use. There is no charge, and we do not save tool inputs or generated results. We value customer privacy and keep building and fixing each day. Always verify important financial, payroll, legal, tax, business, or production-code results before relying on them. If you see an issue, need a tool, or require an update, send feedback to the developer.