See also RFC 1878.
| Hosts | Netmask | Amount of a Class C |
|---|
| /30 | 4 | 255.255.255.252 | 1/64 |
|---|
| /29 | 8 | 255.255.255.248 | 1/32 |
|---|
| /28 | 16 | 255.255.255.240 | 1/16 |
|---|
| /27 | 32 | 255.255.255.224 | 1/8 |
|---|
| /26 | 64 | 255.255.255.192 | 1/4 |
|---|
| /25 | 128 | 255.255.255.128 | 1/2 |
|---|
| /24 | 256 | 255.255.255.0 | 1 |
|---|
| /23 | 512 | 255.255.254.0 | 2 |
|---|
| /22 | 1024 | 255.255.252.0 | 4 |
|---|
| /21 | 2048 | 255.255.248.0 | 8 |
|---|
| /20 | 4096 | 255.255.240.0 | 16 |
|---|
| /19 | 8192 | 255.255.224.0 | 32 |
|---|
| /18 | 16384 | 255.255.192.0 | 64 |
|---|
| /17 | 32768 | 255.255.128.0 | 128 |
|---|
| /16 | 65536 | 255.255.0.0 | 256 |
|---|
Guide to sub-class C blocks
| /25 -- 2 Subnets -- 126 Hosts/Subnet Network # IP Range Broadcast .0 .1-.126 .127 .128 .129-.254 .255 | /30 -- 64 Subnets -- 2 Hosts/Subnet Network # IP Range Broadcast .0 .1-.2 .3 .4 .5-.6 .7 .8 .9-.10 .11 .12 .13-.14 .15 .16 .17-.18 .19 .20 .21-.22 .23 .24 .25-.26 .27 .28 .29-.30 .31 .32 .33-.34 .35 .36 .37-.38 .39 .40 .41-.42 .43 .44 .45-.46 .47 .48 .49-.50 .51 .52 .53-.54 .55 .56 .57-.58 .59 .60 .61-.62 .63 .64 .65-.66 .67 .68 .69-.70 .71 .72 .73-.74 .75 .76 .77-.78 .79 .80 .81-.82 .83 .84 .85-.86 .87 .88 .89-.90 .91 .92 .93-.94 .95 .96 .97-.98 .99 .100 .101-.102 .103 .104 .105-.106 .107 .108 .109-.110 .111 .112 .113-.114 .115 .116 .117-.118 .119 .120 .121-.122 .123 .124 .125-.126 .127 .128 .129-.130 .131 .132 .133-.134 .135 .136 .137-.138 .139 .140 .141-.142 .143 .144 .145-.146 .147 .148 .149-.150 .151 .152 .153-.154 .155 .156 .157-.158 .159 .160 .161-.162 .163 .164 .165-.166 .167 .168 .169-.170 .171 .172 .173-.174 .175 .176 .177-.178 .179 .180 .181-.182 .183 .184 .185-.186 .187 .188 .189-.190 .191 .192 .193-.194 .195 .196 .197-.198 .199 .200 .201-.202 .203 .204 .205-.206 .207 .208 .209-.210 .211 .212 .213-.214 .215 .216 .217-.218 .219 .220 .221-.222 .223 .224 .225-.226 .227 .228 .229-.230 .231 .232 .233-.234 .235 .236 .237-.238 .239 .240 .241-.242 .243 .244 .245-.246 .247 .248 .249-.250 .251 .252 .253-.254 .255 |
| /26 -- 4 Subnets -- 62 Hosts/Subnet Network # IP Range Broadcast .0 .1-.62 .63 .64 .65-.126 .127 .128 .129-.190 .191 .192 .193-.254 .255 |
| /27 -- 8 Subnets -- 30 Hosts/Subnet Network # IP Range Broadcast .0 .1-.30 .31 .32 .33-.62 .63 .64 .65-.94 .95 .96 .97-.126 .127 .128 .129-.158 .159 .160 .161-.190 .191 .192 .193-.222 .223 .224 .225-.254 .255 |
| /28 -- 16 Subnets -- 14 Hosts/Subnet Network # IP Range Broadcast .0 .1-.14 .15 .16 .17-.30 .31 .32 .33-.46 .47 .48 .49-.62 .63 .64 .65-.78 .79 .80 .81-.94 .95 .96 .97-.110 .111 .112 .113-.126 .127 .128 .129-.142 .143 .144 .145-.158 .159 .160 .161-.174 .175 .176 .177-.190 .191 .192 .193-.206 .207 .208 .209-.222 .223 .224 .225-.238 .239 .240 .241-.254 .255 |
| /29 -- 32 Subnets -- 6 Hosts/Subnet Network # IP Range Broadcast .0 .1-.6 .7 .8 .9-.14 .15 .16 .17-.22 .23 .24 .25-.30 .31 .32 .33-.38 .39 .40 .41-.46 .47 .48 .49-.54 .55 .56 .57-.62 .63 .64 .65-.70 .71 .72 .73-.78 .79 .80 .81-.86 .87 .88 .89-.94 .95 .96 .97-.102 .103 .104 .105-.110 .111 .112 .113-.118 .119 .120 .121-.126 .127 .128 .129-.134 .135 .136 .137-.142 .143 .144 .145-.150 .151 .152 .153-.158 .159 .160 .161-.166 .167 .168 .169-.174 .175 .176 .177-.182 .183 .184 .185-.190 .191 .192 .193-.198 .199 .200 .201-.206 .207 .208 .209-.214 .215 .216 .217-.222 .223 .224 .225-.230 .231 .232 .233-.238 .239 .240 .241-.246 .247 .248 .249-.254 .255 |
Taken from: http://www.aelius.com/njh/subnet_sheet.html