Subnetting Table
Use this table to help you calculate Subnet Masks, available hosts per subnet or number of subnets per class. The table deals with Subnetting of only one octet.
| # of Masked bits | # of Non-masked bits | Bit pattern | # of subnets =2^M | What will the new subnet mask be? | # of hosts per subnet (C Class) =[(2^N)-2] |
# of hosts per subnet (B Class) =[(2^N)-2] |
# of hosts per subnet (A Class) =[(2^N)-2] | ||
| None | 0 | 8 | 00000000 | 0 | 0 | 254 | 65,534 | ~16 Million | |
| 1 | 1 | 1 | 7 | 10000000 | 2 | 128 | 126 | 32,766 | ~8 Million |
| 2 | 2 | 2 | 6 | 11000000 | 4 | 192 | 62 | 16,382 | ~4 Million |
| 3 | 4 | 3 | 5 | 11100000 | 8 | 224 | 30 | 8,190 | ~2 Million |
| 4 | 8 | 4 | 4 | 11110000 | 16 | 240 | 14 | 4,094 | ~1 Million |
| 5 | 16 | 5 | 3 | 11111000 | 32 | 248 | 6 | 2,046 | ~520,000 |
| 6 | 32 | 6 | 2 | 11111100 | 64 | 252 | 2 | 1,022 | ~260,000 |
| 7 | 64 | 7 | 1 | 11111110 | 128 | 254 | - | 510 | ~130,000 |
| 8 | 128 | 8 | 0 | 11111111 | 256 | 255 | - | 254 | ~65,000 |
M=Number of Masked bits
N=Number of Non-masked bits - Remember that in Class A and B networks you have other octets besides the one you're subnetting. Therefore in a Class A network instead of saying 7 (for example) you must say 7+8+8. In a Class B network instead of saying 5 (for example again, duh!) you must say 5+8. Only in Class C networks does the N value remain the same.
| Starting bits for the first octet | How many networks per Class? | How many hosts per network? | Range of the first octet | ||
| Class A | 0 | 126 | (2^24)-2=~16 Million | 1-126 | 127=Loopback |
| Class B | 10 | 2^14=16384 | (2^16)-2=~65000 | 128-191 | |
| Class C | 110 | 2^21=~2 Million | (2^8)-2=254 | 192-223 | |
| Class D | 1110 | - | - | 224-239 | |
| Class E | 1111 | - | - | 240-255 |
How many potential IP addresses do we have?
126 networks of 16,777,214 hosts each = 2,113,928,964
16,384 networks of 65,534 hosts each = 1,073,709,056
2,097,152 networks of 254 hosts each = 532,676,608
Total number of hosts = 3,720,314,628