---
canonical: https://openvpn.net/subnet-calculator/
---

# Subnet Calculator

A free, browser-based subnet calculator for IPv4 and IPv6 networks. For IPv4, enter any IP address with a CIDR prefix length or subnet mask to instantly compute the network address, broadcast address, usable host range, subnet mask, and wildcard mask. For IPv6, it identifies the address type and breaks a prefix into /64 (or any smaller) subnets — IPv6 has no broadcast address, so none is shown. All calculations run locally in the browser; no addresses are sent to any server.

## What the tool does

The calculator performs bitwise subnet arithmetic in the browser: it applies the subnet mask to the input address to derive the network address, inverts the mask to find the broadcast address, and counts the usable host range. It supports IPv4 (CIDR and classful notation) and IPv6 prefix lengths from /1 to /128, and includes a CIDR-to-subnet-mask reference table covering every prefix from /0 to /32, and can split any network into its child subnets (e.g. a /24 into four /26s, or a /48 into 65,536 /64s).

## Key facts

- A /24 network has 256 total addresses, 254 usable hosts, subnet mask 255.255.255.0, and wildcard mask 0.0.0.255.
- CIDR notation combines an IP address and prefix length (e.g. 10.0.0.0/16) and replaced the older Class A/B/C system.
- A wildcard mask is the bitwise complement of the subnet mask and is used in router ACLs and OSPF area statements.
- A /30 has 4 total addresses and 2 usable hosts — the classic point-to-point subnet.
- Every standard IPv6 subnet is a /64 — SLAAC requires it; RFC 6164 recommends /127 for IPv6 router point-to-point links. A /48 allocation contains 65,536 /64 subnets.
- A /31 (RFC 3021) is valid for point-to-point links: 2 assignable addresses with no dedicated network or broadcast address.
- Two networks that both use the same private range (e.g. 192.168.1.0/24) normally cannot be routed together — the addresses collide unless one side renumbers or the VPN layer handles the overlap.

## Connecting subnets with CloudConnexa

The page pairs the calculator with CloudConnexa, OpenVPN's cloud-delivered VPN (https://openvpn.net/cloud-vpn/). CloudConnexa can route traffic between networks even when their IP subnets overlap, so sites that share a range can be interconnected without renumbering (https://openvpn.net/use-cases/site-to-site-vpn/). Its full-mesh topology connects every site to every other site and manages the routes automatically (https://openvpn.net/cloud-vpn/features/full-mesh-topology/), and zero-trust access policies can be enforced down to the subnet level (https://openvpn.net/use-cases/zero-trust-network-access/). A free tier is available at https://myaccount.openvpn.com/signup?product=CVPN.