Free tool · IPv4 & IPv6

IP range to CIDR converter

Firewalls, cloud security groups and allowlists expect CIDR notation. Convert any start–end range into CIDR blocks, or see which addresses a block covers.

IP range → CIDR

CIDR → IP range

Building this into an app? Use the IP lookup API and its API quickstart.

Frequently asked questions

How do I convert an IP range to CIDR?

Enter the first and last address. The converter splits the range into the smallest set of CIDR blocks that covers exactly these addresses, e.g. 10.0.0.5–10.0.0.20 becomes five blocks.

Why does a range need several CIDR blocks?

A CIDR block always starts at a multiple of its size. Ranges that do not start and end on such boundaries need several blocks.

IP geolocation API

Get this data in your app

ipbase returns location, ISP, ASN and time zone for any IPv4 or IPv6 address, up to 1,000 addresses per POST request. Security flags (VPN, proxy, Tor, data center) are on the Small plan and above.

Read the documentation

150 free requests every month. No credit card required.

GET https://api.ipbase.com/v2/info?ip=1.1.1.1

{
  "data": {
    "ip": "1.1.1.1",
    "type": "v4",
    "connection": {
      "asn": 13335,
      "organization": "APNIC and Cloudflare DNS Resolver project",
      "isp": "Cloudflare, Inc",
      "range": "1.1.1.0/24"
    },
    "location": {
      "country": { "alpha2": "AU", "name": "Australia" },
      "zip": "4000"
    },
    "security": { "is_vpn": null, "is_tor": null, "threat_score": null }
  }
}

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Example lookups: 8.8.8.8 · 8.8.8.0/24 · AS15169 · example.com · all IPv4 ranges