About CIDR Range Calculator
CIDR Range Calculator takes a block written in CIDR notation — an address followed by a slash and a prefix length, such as 192.168.1.0/24 — and works out the exact span of addresses it covers. It returns the first address in the block, the last address, and the total number of addresses, so you can see at a glance what a subnet does and does not include.
The prefix length is the key that everything else follows from. It states how many of the address leading bits are fixed; the remaining bits are free to vary, and those are the addresses in the block. A /24 fixes the first three octets and leaves the last eight bits free, which yields 256 addresses. A /16 leaves the last sixteen bits free, giving 65,536 addresses. The tool applies this arithmetic by masking the address and computing the floor and ceiling of the range.
The total it reports is the raw address count, before any allowances for the network and broadcast addresses that many configurations reserve. On a /24, for example, the 256 addresses include the network address at the bottom and the broadcast address at the top, which some setups exclude from assignable hosts. Knowing both the full range and the count lets you make that subtraction yourself with the context of your own network.
How to use CIDR Range Calculator
- 1 Type a CIDR block such as 192.168.1.0/24 into the input box.
- 2 Read the address range and the total address count, which update as you type.
- 3 Use the range when planning subnets, firewall rules or routing entries.
Frequently asked questions
What does the /24 in a CIDR block mean?
It is the prefix length — the number of leading bits that are fixed. A /24 fixes the first 24 bits, which are the first three octets, leaving the final octet free to range over 256 addresses.
How many addresses are in a /24?
256. Because 32 minus 24 leaves 8 bits free, and 2 to the power of 8 is 256. A /16 gives 65,536 and a /28 gives 16, each doubling or halving as the prefix changes by one.
Does the total include the network and broadcast addresses?
Yes, the count is the full arithmetic size of the block. On an IPv4 subnet the first address is conventionally the network address and the last the broadcast address, so the number of assignable hosts is usually two fewer.
What does a prefix of 0 or 32 do?
A /0 fixes no bits and covers the entire address space, while a /32 fixes every bit and describes exactly one address. Both are valid inputs and the tool reports the corresponding range and count.
Free, online, and private
Free to use
CIDR Range Calculator is completely free. There is no account to create, no login, and no hidden charge or usage limit.
Runs online in your browser
It is a free online tool that runs entirely in your browser. Nothing to download or install — open the page and start using it right away.
Your data stays private
All processing happens locally on your device. Your input is never uploaded, stored, or tracked, so it never leaves your browser.
How CIDR Range Calculator behaves in detail
These are the specifics of this implementation — the exact ranges, defaults and fixed settings you are working with.
| Parameter | Value |
|---|---|
| Output rows | exactly two: `Range: A - B` and `Total addresses: N` |
| Input split | one text field cut on the first `/` character into an address part and a prefix part |
| Address computation | the network is the address ANDed with a 32-bit mask, the last address is the network ORed with the mask complement |
| Total addresses | end − start + 1, using the full 32-bit address count |
| Prefix zero | handled by a special case that sets the mask to 0, since shifting a 32-bit word by 32 is undefined in JavaScript |
| Sample | 192.168.1.0/24 |
Compiled from the implementation of this tool and checked against it by itoolnet.
What CIDR Range Calculator does not do
Knowing the edges of a tool saves more time than another list of its features. These are the cases where it will not do what you might expect.
- The prefix is never range-checked. It is run straight through parseInt with no clamp, unlike the sibling Subnet Calculator which binds its prefix field to 0 – 32. JavaScript evaluates a shift amount modulo 32, so /33 is treated as a shift of 1 and the block comes back as 128.0.0.0 – 255.255.255.255 holding 2,147,483,648 addresses; /40 is treated as a shift of 8 and reports 192.0.0.0 – 192.255.255.255. Neither is rejected.
- The host range includes the network and the broadcast address. Both ends of the printed range are the reserved addresses of the block, and there is no separate host count that excludes them, so a /24 reads 256 addresses when 254 of them are usable.
- No mask is ever printed. The mask is derived internally to compute the two boundary addresses, but the output has no row for 255.255.255.0 or its prefix length, so anyone who needs the dotted mask still has to work it out elsewhere.
- Only the first slash is honoured. Everything before it is treated as the address and everything after it as the prefix, so a whitespace-padded value keeps the padding and a second slash is carried into the prefix string where parseInt reads just its leading digits.
Tested and documented by itoolnet, the team that builds and maintains this site.