IPv4 Subnet Calculator
Feed a CIDR to get network and broadcast addresses, usable host range and count, subnet mask, IP class and public/private scope; slice finer subnets by a new prefix.
>_ USAGE GUIDE
CIDR is unavoidable when planning networks, VLANs or troubleshooting IP assignments. Enter one CIDR or an IP range and get every network fact instantly.
Typical steps:
- Enter a CIDR: in "Single CIDR" mode type
192.168.1.0/24to get network/broadcast addresses, usable host range and count, subnet mask, prefix, IP class and public/private scope - Range query: switch to "Range query" and type
10.0.0.1 - 10.0.0.50to get the smallest CIDR covering that interval and its facts - Subnet split: in the subnet box enter a finer prefix (e.g. 26) to list the sub-blocks sliced from the network (up to 256 shown)
- IPv6: currently a disabled placeholder — IPv6 math is not yet open
>_ FAQ
Q1 · Why is usable hosts total minus 2?
Each subnet sacrifices the network address (all host bits 0) and the broadcast address (all host bits 1), so usable hosts = 2^hostbits − 2. Exceptions: /31 keeps 2 for point-to-point, /32 is a single host (1).
Q2 · How to tell public from private?
By RFC1918: 10/8, 172.16–31/12 and 192.168/16 are private; 127/8 is loopback, 169.254/16 link-local, 224/4 multicast, 240/4+ reserved, everything else is public.
Q3 · Do IP classes A/B/C still matter?
A/B/C are legacy classes superseded by CIDR, shown only for a rough size estimate, never used in actual routing.
Q4 · Does the range query fit exactly?
The tool prefers the smallest CIDR with capacity ≥ the interval and an aligned start; if the interval cannot be neatly covered (crossing a boundary), the returned CIDR may be larger than your interval — watch the actual coverage.
Q5 · How many subnets are shown?
Up to 256 sub-blocks at once (/24→/30 = 64, /24→/32 = 256 exactly; finer splits show only the first 256), enough for almost any planning scenario.