CIDR Calculator

How to use CIDR Calculator

1. Open CIDR Calculator — it runs entirely in your browser with no setup.
2. Paste or type your input into the text area, or upload a file where supported.
3. Set any options you need. The result appears in the output panel — there is no upload step and no waiting on a server.
4. Review the output instantly; large inputs are handled locally without lag.
5. Copy the result to your clipboard or download it. Your data never leaves the page.

Why use CIDR Calculator?

• 100% free with no limits, no sign-up and no watermarks.
• Private by design — your data are processed in your browser and never uploaded to a server.
• Fast and lightweight, with instant results even on a phone or a slow connection.
• Works everywhere — any modern browser on Windows, macOS, Linux, Android or iOS.
• Part of a full programming suite, so related cidr tasks are one click away.

What people use CIDR Calculator for

• Working out the address range a CIDR block covers.
• Checking whether an IP falls inside a given subnet.
• Planning address allocation for a network.

CIDR Calculator: limits and things worth knowing

• The suffix is the number of fixed network bits: /24 fixes 24 bits and leaves 8 for hosts, giving 256 addresses of which 254 are usable.
• Each step down doubles the block: /23 is 512 addresses, /22 is 1,024. Each step up halves it.
• The first address in a block is the network address and the last is the broadcast address, so usable hosts are always two fewer than the total — except /31, which is defined for point-to-point links.
• IPv6 uses the same notation with 128 bits, where a /64 is the conventional single-subnet size.

Sources

• RFC 4632 — Classless Inter-domain Routing (CIDR)
• RFC 1918 — Address Allocation for Private Internets

Is it private and secure?

Your privacy is built in. CIDR Calculator runs completely on your device, so whatever you enter stays in your browser and is never transmitted, logged or stored on any server.

Network activity: none. Nothing is sent and nothing is fetched. This tool makes no network request at all once the page has loaded — which is why it keeps working if your connection drops.

You do not have to take that on trust — our privacy proof page publishes the Content-Security-Policy that enforces it, lists every third party it permits, and shows how to verify the whole claim yourself.

Learn more

Why Browser-Based Tools Are Safer for Your Files — Most online converters upload your files to a server. Client-side tools don't. Here's why that difference matters for privacy.