/8 · 255.0.0.0
Open in the calculator
A /8 holds 16.7 million addresses. 10.0.0.0/8 is the largest private range (RFC 1918) and the usual starting point for a company-wide address plan, carved into /16 regions and /24 subnets. Public /8s were handed out to early internet organisations and are now scarce.
Key numbers
| Prefix length | /8 (8 network bits, 24 host bits) |
| Subnet mask | 255.0.0.0 |
| Mask in binary | 11111111.00000000.00000000.00000000 |
| Wildcard mask | 0.255.255.255 |
| Total addresses | 16,777,216 |
| Usable hosts | 16,777,214 (total minus network and broadcast) |
| Contains | 65,536 × /24 networks |
| Block size | Increments of 1 in octet 1 |
Example ranges
Private (RFC 1918) blocks of this size. Click one to open it in the calculator.
| Block | First address | Last address | Usable hosts |
|---|---|---|---|
| 10.0.0.0/8 | 10.0.0.0 | 10.255.255.255 | 10.0.0.1 – 10.255.255.254 |
Usable addresses in the cloud
Cloud providers reserve a few addresses in every subnet for the router, DNS and future use, so the usable count is lower than the formula gives.
| Provider | Usable in a /8 | Notes |
|---|---|---|
| AWS VPC subnet | n/a | Not allowed: AWS subnets must be between /16 and /28. |
| Azure virtual network subnet | 16,777,211 | Allowed. Azure reserves the first four addresses and the last one. |
| Google Cloud subnet | 16,777,212 | Allowed. Google Cloud reserves the first two and the last two addresses. |
How the numbers are derived
An IPv4 address has 32 bits. A /8 uses 8 of them for the network, leaving 24 host bits, so the block has 224 = 16,777,216 addresses. The first address (all host bits 0) is the network address and the last (all host bits 1) is the broadcast address, which leaves 16,777,214 for hosts. The subnet mask is 8 ones followed by 24 zeros, written in dotted decimal as 255.0.0.0; the wildcard mask 0.255.255.255 is its inverse, used in Cisco ACLs and OSPF configuration.
FAQ
How many hosts can a /8 have?
16,777,216 addresses in total, of which 16,777,214 are usable after removing the network and broadcast addresses. Cloud providers reserve a few more: 16,777,211 usable in AWS and Azure, 16,777,212 in Google Cloud.
How many /24 subnets fit in a /8?
65,536. Each step of the prefix length halves or doubles the block, so a /8 contains 2^(24 − 8) = 65,536 networks of /24 size.