192.168.0.0/24
About CIDR Calculator — Merge, Split & Aggregate
CIDR notation (like 10.0.0.0/24) is how networks describe a block of IP addresses with a single prefix. Over time, route tables, firewall rules, and allow-lists fill up with blocks that overlap or sit right next to each other — and sometimes you need to carve one block into smaller, equal pieces. This CIDR merge and split tool handles both jobs with pure address math.
Merge mode takes a list of IPv4 CIDRs and aggregates every adjacent or overlapping block into the smallest equivalent set, dropping anything already contained in a larger range. Split mode takes one block and divides it into 2, 4, 8 or more equal subnets at a longer prefix — the quick way to subnet a network for VLANs, environments, or tenants.
Everything runs offline in your browser. The CIDRs you paste are never uploaded, logged, or sent to a server, so it is safe to use with internal address plans.
Features
- Merge overlapping and adjacent IPv4 CIDRs into the minimal covering set
- Split one block into equal subnets at any longer prefix
- Normalizes host addresses to their network base (10.0.0.5/24 → 10.0.0.0/24)
- Clear errors on invalid input; fully offline — nothing leaves your device
How to use
- Pick Merge or Split with the toggle in the toolbar.
- For Merge, paste your CIDRs one per line; for Split, enter one CIDR and choose the new prefix with the stepper.
- Read the aggregated or subnetted blocks in the output pane.
- Copy the result, or clear the input and start again.
Frequently asked questions
What does merging or aggregating CIDRs mean?
Aggregation replaces several CIDR blocks with the fewest blocks that cover exactly the same addresses. Two adjacent /25 halves of a /24, for example, collapse into a single /24. It shrinks route tables and firewall rules without changing what they match.
How many subnets do I get when I split a block?
Splitting from a /p block to a /n prefix produces 2^(n − p) equal subnets. A /24 split at /26 gives 4 subnets; at /28 it gives 16. The target prefix must be greater than or equal to the original prefix and no larger than /32.
Why was my CIDR rewritten with a different address?
A CIDR identifies a network, so the tool masks the host bits off and shows the network base. 10.0.0.5/24 covers the same range as 10.0.0.0/24, so it is normalized to 10.0.0.0/24 before merging or splitting.
Does this support IPv6?
Not yet — this tool works on IPv4 CIDRs using 32-bit address math. IPv6 uses 128-bit addresses and a different notation.
Is my address plan sent anywhere?
No. All parsing and arithmetic happen locally in your browser. The CIDRs you enter never leave your device, which makes the tool safe for internal or private network plans.
Related tools
Everything runs locally in your browser — your input is never uploaded.