IP Range to CIDR
Enter the first and last address of a range.
CIDR blocks (18)
- 10.0.0.1/32
- 10.0.0.2/31
- 10.0.0.4/30
- 10.0.0.8/29
- 10.0.0.16/28
- 10.0.0.32/27
- 10.0.0.64/26
- 10.0.0.128/25
- 10.0.1.0/24
- 10.0.2.0/24
- 10.0.3.0/25
- 10.0.3.128/26
- 10.0.3.192/27
- 10.0.3.224/28
- 10.0.3.240/29
- 10.0.3.248/30
- 10.0.3.252/31
- 10.0.3.254/32
Firewalls, cloud security groups and routing configs usually want CIDR blocks, but allocations are often described as a start and end address. This tool finds the smallest set of aligned CIDR blocks that covers the range exactly — no more, no less.
A range that starts and ends on a block boundary becomes a single prefix (10.0.0.0 – 10.0.3.255 is 10.0.0.0/22). Unaligned ranges need several blocks.
Frequently asked questions
Why does my range produce several CIDR blocks?
A CIDR block must start at a multiple of its size. If your range starts or ends between those boundaries, it has to be covered by several smaller blocks.
Does this work for IPv6?
Yes. Both addresses must be the same version.