Subnet Calculator

Plan IP subnets based on host requirements. Calculate optimal subnet masks, determine network boundaries, and visualize subnet allocation. Perfect for network design and VLSM planning.

Network Requirements

Base Network

Network address with prefix (CIDR notation)

Required Hosts per Subnet

Number of usable host IPs needed

Number of Subnets

Growth Margin (%)

Reserve capacity for future expansion

Recommended Subnet Configuration

Subnet Mask

Prefix Length

Hosts per Subnet

Total Subnets

Wildcard Mask

Usable IPs

Utilization

Subnet Breakdown

Quick Reference

Prefix	Subnet Mask	Wildcard	Usable Hosts	Typical Use
/30	255.255.255.252	0.0.0.3	2	Point-to-point links
/29	255.255.255.248	0.0.0.7	6	Very small networks
/28	255.255.255.240	0.0.0.15	14	Small office
/27	255.255.255.224	0.0.0.31	30	Department
/26	255.255.255.192	0.0.0.63	62	Medium office
/25	255.255.255.128	0.0.0.127	126	Large office
/24	255.255.255.0	0.0.0.255	254	Standard LAN
/23	255.255.254.0	0.0.1.255	510	Large campus

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Frequently Asked Questions

Count required hosts, add growth margin (20-50%), add 2 for network/broadcast. Use next power of 2. For 50 hosts, you need 64 IPs (/26). For 200 hosts, use 256 IPs (/24).

They're equivalent. /24 = 255.255.255.0. /16 = 255.255.0.0. Prefix counts network bits (24 means first 24 bits are network). Subnet mask shows the same in dotted decimal.

Increase the prefix. /24 (254 hosts) → two /25 (126 each), four /26 (62 each), eight /27 (30 each). Each +1 to prefix halves the number of hosts and doubles subnet count.

Variable Length Subnet Masking (VLSM) uses different subnet sizes for different needs. Allocate /30 for point-to-point links (2 hosts), /27 for small offices (30 hosts), /24 for departments (254 hosts). Saves IP space.

From /24: you can create 2 /25s, 4 /26s, 8 /27s, 16 /28s, 32 /29s, 64 /30s, or 128 /31s. Each additional prefix bit doubles the number of subnets and halves hosts per subnet.

Total IPs = 2^(32-prefix). Usable = total - 2 (minus network and broadcast addresses). A /24 has 256 total, 254 usable. Exception: /31 for point-to-point links has 2 usable (no broadcast).

Ensure subnet ranges don't intersect. Plan from largest to smallest. If you allocate 10.0.0.0/24, next subnet must start at 10.0.1.0 or later. Use a subnet calculator or IP Address Management (IPAM) tool.

Depends on devices. Typical: 20-50 employees = /27 or /26 (30-62 hosts). Add 30-50% growth margin. Consider VoIP phones, printers, IoT—each device needs an IP. /24 gives plenty of room.

Yes (RFC 3021). /31 gives 2 usable IPs with no broadcast—perfect for router-to-router links. Saves IPs vs /30 (which wastes 2 IPs). Both Cisco and Juniper support /31 on modern gear.

Find the common prefix bits across networks. If combining 192.168.0.0/24, 192.168.1.0/24, 192.168.2.0/24, 192.168.3.0/24, they summarize to 192.168.0.0/22. Look for the longest common prefix.

Network Requirements

Recommended Subnet Configuration

Subnet Breakdown

Quick Reference

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