# Subnet calculator: run it free, or from your agent

IPv4 CIDR and mask calculator: network, broadcast, host range, wildcard, host count and a split into smaller subnets.

## Prompt

Use looot to check who owns the addresses in a network block. 1. Set up https://looot.ai/skill.md. 2. Work out the first and last usable host of [CIDR, for example 203.0.113.0/28]. 3. Search the catalog for an IP lookup endpoint and check its price before you call. 4. Look up the first and last host. 5. Return the owner, country and network type for each.

## What it needs

An IPv4 address with a CIDR prefix or a subnet mask

## What comes back

- network and broadcast address
- first and last usable host
- subnet and wildcard mask
- usable host count
- list of smaller subnets

## Endpoints and providers

None. The tool on the web page runs in the browser and calls no endpoint.

## What it costs

Nothing. The tool on the web page runs in the visitor's browser: no account, no API call and no limit per hour. The prompt above runs the same job from your own looot account with current data, billed per call.

## Plan a VPC

Split a /16 into /24 subnets for each zone and copy the list as CSV.

## Write firewall rules

Get the wildcard mask for an ACL or check the range a rule covers.

## Read a CIDR

See at once how many hosts a /27 holds and where it starts and ends.

## Study for exams

Check subnetting answers with the address and mask in binary.

## How do I calculate a subnet?

Apply the mask to the address with a bitwise AND to get the network address. Set all host bits to 1 for the broadcast address. The hosts are everything in between. Type the address and prefix here and every value appears.

## How many usable hosts are in a /24?

254. A /24 has 256 addresses, and the network and broadcast addresses are not assigned to hosts. In general a prefix of n gives 2 to the power of (32 minus n) addresses, minus 2.

## What about /31 and /32?

A /31 has two addresses and RFC 3021 lets both be used on a point to point link. A /32 is one host. The page counts every address in these as usable.

## Can I enter a subnet mask instead of a prefix?

Yes. Type the address, a space and the mask, such as 10.0.0.5 255.255.252.0. A mask with gaps in its 1 bits is rejected because it is not a valid subnet mask.

## What is a wildcard mask?

The inverse of the subnet mask: 0.0.0.255 for a /24. Cisco ACLs and OSPF use it to say which bits may vary.

## How do I split a network into smaller subnets?

Pick a longer prefix under Split. A /22 split into /24 gives four subnets. The table lists up to 256 rows, and the CSV holds the same rows.

## Does it support IPv6?

No, IPv4 only for now. An IPv6 address is rejected with an error.

## Does it tell me if an address is private?

Yes. Address type shows private (RFC 1918), carrier-grade NAT, loopback, link-local, multicast or public.

## Related tools

- /free-tools/ip-lookup
- /free-tools/binary-to-text
- /free-tools/unix-timestamp-converter

## Last reviewed

2026-10-14.