/20 at a glance
| Netmask | 255.255.240.0 |
|---|
| Wildcard mask | 0.0.15.255 |
|---|
| Binary | 11111111.11111111.11110000.00000000 |
|---|
| Total addresses | 4,096 |
|---|
| Usable hosts | 4,094 |
|---|
| /20s in a /16 | 16 |
|---|
| /20s in a /8 | 4,096 |
|---|
Cloud note: AWS reserves 5 addresses in every VPC subnet, and Azure reserves 5 too, so usable hosts in a cloud subnet are total − 5.
CIDR prefix table
| Prefix | Netmask | Addresses |
|---|
| /8 |
255.0.0.0 |
16,777,216 |
| /12 |
255.240.0.0 |
1,048,576 |
| /16 |
255.255.0.0 |
65,536 |
| /20 |
255.255.240.0 |
4,096 |
| /22 |
255.255.252.0 |
1,024 |
| /23 |
255.255.254.0 |
512 |
| /24 |
255.255.255.0 |
256 |
| /25 |
255.255.255.128 |
128 |
| /26 |
255.255.255.192 |
64 |
| /27 |
255.255.255.224 |
32 |
| /28 |
255.255.255.240 |
16 |
| /29 |
255.255.255.248 |
8 |
| /30 |
255.255.255.252 |
4 |
| /31 |
255.255.255.254 |
2 |
| /32 |
255.255.255.255 |
1 |
Private ranges (RFC 1918)
10.0.0.0/8 — 16.7 million addresses172.16.0.0/12 — 1 million addresses192.168.0.0/16 — 65,536 addresses100.64.0.0/10 — carrier-grade NAT (RFC 6598), also used by Tailscale