IP Block Calculator

Formula used

• Network = IP AND SubnetMask
• Wildcard = NOT SubnetMask (limited to 32 bits)
• Broadcast = Network OR Wildcard
• Total addresses = 2^(32 - prefix)
• Usable hosts = Total - 2 (except /31 and /32 rules)
• Range → CIDR uses the largest aligned block that fits the remaining range.

How to use this calculator

1. Select an input method (CIDR, mask, prefix, or range).
2. Enter the requested fields for that method.
3. Enable options if you need binary or hex details.
4. Click Calculate to view results above the form.
5. Use Download CSV or Download PDF for reports.

FAQs

1) What is an IP block?

An IP block is a contiguous set of IPv4 addresses defined by a network boundary. It is typically expressed as CIDR and used for routing, DHCP scopes, firewall rules, and access control lists.

2) What does CIDR mean?

CIDR is a compact notation that combines an IP with a prefix length, like 192.168.1.0/24. The prefix tells how many bits represent the network portion, and the remaining bits represent host addresses.

3) How are network and broadcast addresses calculated?

The network address is found by applying a bitwise AND between the IP and subnet mask. The broadcast address is the network address OR the wildcard mask (the inverted subnet mask) within 32 bits.

4) Why do usable hosts differ for /31 and /32?

Traditionally, two addresses are reserved (network and broadcast). A /32 is a single host route, so it has one address. Many networks treat /31 as point‑to‑point, allowing both addresses to be used.

5) Can I convert a start-to-end range into CIDR blocks?

Yes. Choose the range method, enter start and end IPs, and the tool outputs a minimal list of CIDR blocks that exactly covers the range without adding extra addresses.

6) What is a wildcard mask used for?

A wildcard mask is the inverse of the subnet mask. It is commonly used in access control lists to match address patterns, where 0 bits must match and 1 bits are treated as “don’t care.”

7) Why must subnet masks be contiguous?

Valid IPv4 subnet masks are a sequence of 1 bits followed by 0 bits. Non‑contiguous masks break the definition of a single network prefix and can produce inconsistent routing and address calculations.

8) How can I use results for blocking or allowing traffic?

Use the computed CIDR for firewall or proxy rules to represent the whole block. For systems that require start/end ranges, use first and last usable addresses, or use the range mode to generate multiple CIDRs.