CIDR Subnet Calculator & DNS Lookup Online
Compute subnet ranges from CIDR notation and perform quick domain lookups with this free online network tool. Enter a block like 192.168.1.0/24 and instantly see the network address, broadcast address, usable host range, subnet mask, and total host count — the numbers you need for firewall rules, VPC design, and IP allocation planning.
CIDR math is easy to get wrong by hand and expensive to get wrong in production: an off-by-one subnet boundary can overlap VPCs or blackhole traffic. This calculator does the binary arithmetic for you, while the DNS lookup side quickly maps domain names for debugging connectivity and configuration issues.
How to Calculate a CIDR Subnet
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Enter the CIDR block
Type an IP with prefix length, e.g. 10.0.0.0/16 or 192.168.1.0/24.
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Read the results
See the network address, broadcast address, first and last usable hosts, subnet mask, and host count instantly.
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Plan your ranges
Adjust the prefix length to size subnets for your VPC, VLAN, or firewall rules.
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Look up domains
Switch to the lookup mode to resolve domain names while debugging connectivity.
Features of the Network Toolkit
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Full CIDR breakdown
Network, broadcast, usable range, netmask, wildcard mask, and host counts from any prefix.
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Any prefix length
From /8 corporate blocks to /30 point-to-point links — the math is instant and exact.
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DNS lookups included
Resolve domains alongside subnet planning without switching tools.
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Cloud-network friendly
Perfect for sizing AWS VPCs, GCP subnets, and Kubernetes pod CIDR ranges.
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No installation
Subnetting answers in the browser — no ipcalc install, no man pages.
Frequently Asked Questions
What does the /24 in CIDR notation mean?
The prefix length — how many leading bits of the address identify the network. /24 fixes the first 24 bits (three octets), leaving 8 bits for hosts: 256 addresses, 254 usable (network and broadcast are reserved).
How many hosts fit in each common subnet?
Usable hosts = 2^(32 − prefix) − 2. So /30 = 2, /29 = 6, /28 = 14, /27 = 30, /26 = 62, /25 = 126, /24 = 254, /16 = 65,534. The calculator shows this for any prefix instantly.
What is the difference between network and broadcast addresses?
The network address (all host bits 0) identifies the subnet itself; the broadcast address (all host bits 1) reaches every host in it. Neither can be assigned to a device, which is why usable hosts are total minus two.
Which IP ranges are private?
RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 for private networks. These are the ranges you subnet inside home networks, offices, and cloud VPCs.
How do I avoid overlapping subnets in cloud VPCs?
Plan top-down: pick one large block per VPC (e.g. 10.0.0.0/16), carve non-overlapping child subnets (10.0.0.0/24, 10.0.1.0/24 …), and verify each boundary here before applying — overlaps break routing and peering.