CIDR Utilization Cheat Sheet
class C's Hosts 80% 50% 25% /32 1/256 1 /31 1/128 2 /30 1/64 4 /29 1/32 8 6 4 2 /28 1/16 16 13 8 4 /27 1/8 32 25 16 8 /26 1/4 64 51 32 16 /25 1/2 128 102 64 32 /24 1C 256 204 128 64 /23 2C 512 410 256 128 /22 4C 1024 819 512 256 /21 8C 2048 1638 1024 512 /20 16C 4096 3277 2048 1024 /19 32C 8192 6553 4096 2048 /18 64C 16384 13107 8192 4096 /17 128C 32768 26214 16384 8192 /16 B - 256C 65536 52429 32768 16384 /15 2B - 512C 131072 104858 65536 32768 /14 4B - 1024C 262144 209715 131072 65536 /13 8B - 2048C 524288 419430 262144 131072 /12 16B - 4096C 1048576 838860 524288 262144 /11 32B - 8192C 2097152 1677721 1048576 524288 /10 64B - 16384C 4194304 3355443 2097152 1048576
Starting boundaries for different size CIDR blocks
/32's /31's /30's /29's /28's /27's /26's /25's /24's /23's /22's /21's /20's /19's /18's /17's ----- ----- ------ ------ ------- ------- ------- ------- 0 0 0 0 0 0 0 0 1 2 4 8 16 32 64 128 2 4 8 16 32 64 128 3 6 12 24 48 96 192 4 8 16 32 64 128 5 10 20 40 80 160 6 12 24 48 96 192 7 14 28 56 112 224 8 16 32 64 128 9 18 36 72 144 10 20 40 80 160 11 22 44 88 176 12 24 48 96 192 13 26 52 104 208 14 28 56 112 224 15 30 60 120 240 16 32 64 128 17 34 68 136 18 36 72 144 19 38 76 152 20 40 80 160 21 42 84 168 22 44 88 176 23 46 92 184 24 48 96 192 25 50 100 200 26 52 104 208 27 54 108 216 28 56 112 224 29 58 116 232 etc etc etc etc
IPv6
2^64 = 18,446,744,073,709,551,616
Prefix /32 count /48 count /56 count Number of /64 Subnets Number of Hosts
/56 1 256 4,722,366,482,869,645,213,696 (2^72)
/55 2 512 9,444,732,965,739,290,427,392
/54 4 1,024 18,889,465,931,478,580,854,784
/53 8 2,048 37,778,931,862,957,161,709,568
/52 16 4,096 75,557,863,725,914,323,419,136
/51 32 8,192 151,115,727,451,828,646,838,272
/50 64 16,384 302,231,454,903,657,293,676,544
/49 128 32,768 604,462,909,807,314,587,353,088
/48 1 256 65,536 1,208,925,819,614,629,174,706,176 (2^80)
/47 2 512 131,072 2,417,851,639,229,258,349,412,352
/46 4 1,024 262,144 4,835,703,278,458,516,698,824,704
/45 8 2,048 524,288 9,671,406,556,917,033,397,649,408
/44 16 4,096 1,048,576 19,342,813,113,834,066,795,298,816
/43 32 8,192 2,097,152 38,685,626,227,668,133,590,597,632
/42 64 16,384 4,194,304 77,371,252,455,336,267,181,195,264
/41 128 32,768 8,388,608 154,742,504,910,672,534,362,390,528
/40 256 65,536 16,777,216 309,485,009,821,345,068,724,781,056
/39 512 131,072 33,554,432 618,970,019,642,690,137,449,562,112
/38 1,024 262,144 67,108,864 1,237,940,039,285,380,274,899,124,224
/37 2,048 524,288 134,217,728 2,475,880,078,570,760,549,798,248,448
/36 4,096 1,048,576 268,435,456 4,951,760,157,141,521,099,596,496,896
/35 8,192 2,097,152 536,870,912 9,903,520,314,283,042,199,192,993,792
/34 16,384 4,194,304 1,073,741,824 19,807,040,628,566,084,398,385,987,584
/33 32,768 8,388,608 2,147,483,648 39,614,081,257,132,168,796,771,975,168
/32 1 65,536 16,777,216 4,294,967,296 79,228,162,514,264,337,593,543,950,336 (2^96)
/31 2 131,072 33,554,432 8,589,934,592 158,456,325,028,528,675,187,087,900,672
/30 4 262,144 67,108,864 17,179,869,184 316,912,650,057,057,350,374,175,801,344
/29 8 524,288 134,217,728 34,359,738,368 633,825,300,114,114,700,748,351,602,688
/28 16 1,048,576 268,435,456 68,719,476,736 1,267,650,600,228,229,401,496,703,205,376
/27 32 2,097,152 536,870,912 137,438,953,472 2,535,301,200,456,458,802,993,406,410,752
/26 64 4,194,304 1,073,741,824 274,877,906,944 5,070,602,400,912,917,605,986,812,821,504
/25 128 8,388,608 2,147,483,648 549,755,813,888 10,141,204,801,825,835,211,973,625,643,008
/24 256 16,777,216 4,294,967,296 1,099,511,627,776 20,282,409,603,651,670,423,947,251,286,016
/23 512 33,554,432 8,589,934,592 2,199,023,255,552 40,564,819,207,303,340,847,894,502,572,032
/22 1024 67,108,864 17,179,869,184 4,398,046,511,104 81,129,638,414,606,681,695,789,005,144,064
/21 2048 134,217,728 34,359,738,368 8,796,093,022,208 162,259,276,829,213,363,391,578,010,288,128
/20 4096 268,435,456 68,719,476,736 17,592,186,044,416 324,518,553,658,426,726,783,156,020,576,256
/19 8192 536,870,912 137,438,953,472 35,184,372,088,832 649,037,107,316,853,453,566,312,041,152,512
/18 16384 1,073,741,824 274,877,906,944 70,368,744,177,664 1,298,074,214,633,706,907,132,624,082,305,024
/17 32768 2,147,483,648 549,755,813,888 140,737,488,355,328 2,596,148,429,267,413,814,265,248,164,610,048
/16 65536 4,294,967,296 1,099,511,627,776 281,474,976,710,656 5,192,296,858,534,827,628,530,496,329,220,096
/15 131072 8,589,934,592 2,199,023,255,552 562,949,953,421,312 1,038,459,371,706,965,525,706,099,265,844,0192
/14 262144 17,179,869,184 4,398,046,511,104 1,125,899,906,842,624 207,691,874,341,393,105,141,219,853,168,80,384
/13 524288 34,359,738,368 8,796,093,022,208 2,251,799,813,685,248 41,538,374,868,278,621,028,243,970,633,760,768
/12 1048576 68,719,476,736 17,592,186,044,416 4,503,599,627,370,496 83,076,749,736,557,242,056,487,941,267,521,536
/11 2097152 137,438,953,472 35,184,372,088,832 9,007,199,254,740,992 166,153,499,473,114,484,112,975,882,535,043,072
/10 4194304 274,877,906,944 70,368,744,177,664 18,014,398,509,481,984 332,306,998,946,228,968,225,951,765,070,086,144
/9 8388608 549,755,813,888 140,737,488,355,328 36,028,797,018,963,968 664,613,997,892,457,936,451,903,530,140,172,288
/8 16777216 1,099,511,627,776 281,474,976,710,656 72,057,594,037,927,936 1,329,227,995,784,915,872,903,807,060,280,344,576
/7 33554432 2,199,023,255,552 562,949,953,421,312 144,115,188,075,855,872 2,658,455,991,569,831,745,807,614,120,560,689,152
/6 67108864 4,398,046,511,104 1,125,899,906,842,624 288,230,376,151,711,744 5,316,911,983,139,663,491,615,228,241,121,378,304
/5 134217728 8,796,093,022,208 2,251,799,813,685,248 576,460,752,303,423,488 10,633,823,966,279,326,983,230,456,482,242,756,608
/4 268435456 17,592,186,044,416 4,503,599,627,370,496 1,152,921,504,606,846,976 21,267,647,932,558,653,966,460,912,964,485,513,216
/3 536870912 35,184,372,088,832 9,007,199,254,740,992 2,305,843,009,213,693,952 42,535,295,865,117,307,932,921,825,928,971,026,432
/2 1073741824 70,368,744,177,664 18,014,398,509,481,984 4,611,686,018,427,387,904 85,070,591,730,234,615,865,843,651,857,942,052,864
/1 2147483648 140,737,488,355,328 36,028,797,018,963,968 9,223,372,036,854,775,808 170,141,183,460,469,231,731,687,303,715,884,105,728
