Local network calculator
IPv4 subnet and CIDR calculator
Calculate an IPv4 CIDR network, subnet mask, broadcast address, address count and usable range locally in your browser. Handles /31 and /32 explicitly.
Calculate an IPv4 subnet
Enter an IPv4 address and a CIDR prefix from /0 through /32. The calculation runs in this browser; the address is not looked up or sent anywhere.
Use dotted decimal, for example 192.0.2.17. Do not include a slash in the address field.
How to read the result
The network address is the first address in the block. The directed broadcast address is the last address for prefixes through /30. The conventional usable range excludes those two addresses, which is why a typical /24 has 254 host addresses.
/31 blocks have two usable addresses on point-to-point links under RFC 3021. A /32 identifies one address, often used as a host route. The calculator reports these cases separately instead of applying the usual network/broadcast subtraction.
This is address arithmetic only. It does not check whether a block is assigned, routable, available on your network, or safe to configure. Confirm network plans with the responsible administrator.
When reviewing a VPN route list, calculate each IPv4 prefix separately and compare the resulting ranges against the approved plan. This page does not compare multiple entries or inspect installed routes; see the Windows VPN route-based split tunneling guide for policy checks and managed-device cautions.
Source
- IETF RFC 4632: Classless Inter-domain Routing (CIDR) (2006-08). Defines CIDR prefixes and address aggregation.
- IETF RFC 3021: Using 31-Bit Prefixes on IPv4 Point-to-Point Links (2000-12). Defines use of both addresses in a /31 point-to-point link.
Related: IPv6 prefix range calculator and address validator, IP and DNS checks, and the IP geolocation accuracy guide.
How it works
Enter an IPv4 address and a prefix from /0 to /32. The calculator performs local address arithmetic; it does not check allocation, routing, or availability on a network.
Good to know
Does this calculator send or look up my IP address?
No. The entered address is processed in your browser and is not used for a network lookup.
How are /31 and /32 handled?
A /31 reports both addresses as usable for a point-to-point link under RFC 3021. A /32 is reported as one host address with no directed broadcast.
Does the result tell me whether this subnet is available?
No. It only calculates address boundaries. Check your network plan and administrator for assignments, overlaps, and routing.
Impact — TODO: apply/approval and configure referral URL — referral link not configured.
PartnerStack — TODO: apply/approval and configure referral URL — referral link not configured.
CJ Affiliate — TODO: apply/approval and configure referral URL — referral link not configured.