IPv4 Subnet Calculator

Enter an IP with a CIDR prefix or a subnet mask to see its network, broadcast, host range, and host count. You can also split the network into smaller subnets.

Try:192.168.1.10/24 10.0.0.0/8 172.16.5.4/20 203.0.113.9/29

IPv6 calculator →

private IP (RFC 1918)10.0.128.0/21

network10.0.128.0/21

broadcast10.0.135.255

first host10.0.128.1

last host10.0.135.254

subnet mask255.255.248.0

wildcard0.0.7.255

addresses2,048

usable hosts2,046

classA

ipcalc 10.0.128.0/21

address00001010.00000000.10000000.00000000

subnet mask11111111.11111111.11111000.00000000

network00001010.00000000.10000000.00000000

broadcast00001010.00000000.10000111.11111111

green = network part, grey = host part

hex0x0a008000

decimal167804928

reverse dns0.128.0.10.in-addr.arpa

ipv4-mapped::ffff:a00:8000

/21 split into /27 · 64 subnets

close ×

#	network	host range	broadcast
1	10.0.128.0/27	10.0.128.1 – 10.0.128.30	10.0.128.31
2	10.0.128.32/27	10.0.128.33 – 10.0.128.62	10.0.128.63
3	10.0.128.64/27	10.0.128.65 – 10.0.128.94	10.0.128.95
4	10.0.128.96/27	10.0.128.97 – 10.0.128.126	10.0.128.127
5	10.0.128.128/27	10.0.128.129 – 10.0.128.158	10.0.128.159
6	10.0.128.160/27	10.0.128.161 – 10.0.128.190	10.0.128.191
7	10.0.128.192/27	10.0.128.193 – 10.0.128.222	10.0.128.223
8	10.0.128.224/27	10.0.128.225 – 10.0.128.254	10.0.128.255
9	10.0.129.0/27	10.0.129.1 – 10.0.129.30	10.0.129.31
10	10.0.129.32/27	10.0.129.33 – 10.0.129.62	10.0.129.63
11	10.0.129.64/27	10.0.129.65 – 10.0.129.94	10.0.129.95
12	10.0.129.96/27	10.0.129.97 – 10.0.129.126	10.0.129.127
13	10.0.129.128/27	10.0.129.129 – 10.0.129.158	10.0.129.159
14	10.0.129.160/27	10.0.129.161 – 10.0.129.190	10.0.129.191
15	10.0.129.192/27	10.0.129.193 – 10.0.129.222	10.0.129.223
16	10.0.129.224/27	10.0.129.225 – 10.0.129.254	10.0.129.255
17	10.0.130.0/27	10.0.130.1 – 10.0.130.30	10.0.130.31
18	10.0.130.32/27	10.0.130.33 – 10.0.130.62	10.0.130.63
19	10.0.130.64/27	10.0.130.65 – 10.0.130.94	10.0.130.95
20	10.0.130.96/27	10.0.130.97 – 10.0.130.126	10.0.130.127
21	10.0.130.128/27	10.0.130.129 – 10.0.130.158	10.0.130.159
22	10.0.130.160/27	10.0.130.161 – 10.0.130.190	10.0.130.191
23	10.0.130.192/27	10.0.130.193 – 10.0.130.222	10.0.130.223
24	10.0.130.224/27	10.0.130.225 – 10.0.130.254	10.0.130.255
25	10.0.131.0/27	10.0.131.1 – 10.0.131.30	10.0.131.31
26	10.0.131.32/27	10.0.131.33 – 10.0.131.62	10.0.131.63
27	10.0.131.64/27	10.0.131.65 – 10.0.131.94	10.0.131.95
28	10.0.131.96/27	10.0.131.97 – 10.0.131.126	10.0.131.127
29	10.0.131.128/27	10.0.131.129 – 10.0.131.158	10.0.131.159
30	10.0.131.160/27	10.0.131.161 – 10.0.131.190	10.0.131.191
31	10.0.131.192/27	10.0.131.193 – 10.0.131.222	10.0.131.223
32	10.0.131.224/27	10.0.131.225 – 10.0.131.254	10.0.131.255
33	10.0.132.0/27	10.0.132.1 – 10.0.132.30	10.0.132.31
34	10.0.132.32/27	10.0.132.33 – 10.0.132.62	10.0.132.63
35	10.0.132.64/27	10.0.132.65 – 10.0.132.94	10.0.132.95
36	10.0.132.96/27	10.0.132.97 – 10.0.132.126	10.0.132.127
37	10.0.132.128/27	10.0.132.129 – 10.0.132.158	10.0.132.159
38	10.0.132.160/27	10.0.132.161 – 10.0.132.190	10.0.132.191
39	10.0.132.192/27	10.0.132.193 – 10.0.132.222	10.0.132.223
40	10.0.132.224/27	10.0.132.225 – 10.0.132.254	10.0.132.255
41	10.0.133.0/27	10.0.133.1 – 10.0.133.30	10.0.133.31
42	10.0.133.32/27	10.0.133.33 – 10.0.133.62	10.0.133.63
43	10.0.133.64/27	10.0.133.65 – 10.0.133.94	10.0.133.95
44	10.0.133.96/27	10.0.133.97 – 10.0.133.126	10.0.133.127
45	10.0.133.128/27	10.0.133.129 – 10.0.133.158	10.0.133.159
46	10.0.133.160/27	10.0.133.161 – 10.0.133.190	10.0.133.191
47	10.0.133.192/27	10.0.133.193 – 10.0.133.222	10.0.133.223
48	10.0.133.224/27	10.0.133.225 – 10.0.133.254	10.0.133.255
49	10.0.134.0/27	10.0.134.1 – 10.0.134.30	10.0.134.31
50	10.0.134.32/27	10.0.134.33 – 10.0.134.62	10.0.134.63
51	10.0.134.64/27	10.0.134.65 – 10.0.134.94	10.0.134.95
52	10.0.134.96/27	10.0.134.97 – 10.0.134.126	10.0.134.127
53	10.0.134.128/27	10.0.134.129 – 10.0.134.158	10.0.134.159
54	10.0.134.160/27	10.0.134.161 – 10.0.134.190	10.0.134.191
55	10.0.134.192/27	10.0.134.193 – 10.0.134.222	10.0.134.223
56	10.0.134.224/27	10.0.134.225 – 10.0.134.254	10.0.134.255
57	10.0.135.0/27	10.0.135.1 – 10.0.135.30	10.0.135.31
58	10.0.135.32/27	10.0.135.33 – 10.0.135.62	10.0.135.63
59	10.0.135.64/27	10.0.135.65 – 10.0.135.94	10.0.135.95
60	10.0.135.96/27	10.0.135.97 – 10.0.135.126	10.0.135.127
61	10.0.135.128/27	10.0.135.129 – 10.0.135.158	10.0.135.159
62	10.0.135.160/27	10.0.135.161 – 10.0.135.190	10.0.135.191
63	10.0.135.192/27	10.0.135.193 – 10.0.135.222	10.0.135.223
64	10.0.135.224/27	10.0.135.225 – 10.0.135.254	10.0.135.255

01 / table

IPv4 CIDR prefix table.

Click a prefix longer than your network to split it into subnets.

prefix	subnet mask	addresses	hosts	in your /21
/0	0.0.0.0	4,294,967,296	4,294,967,294	-
/1	128.0.0.0	2,147,483,648	2,147,483,646	-
/2	192.0.0.0	1,073,741,824	1,073,741,822	-
/3	224.0.0.0	536,870,912	536,870,910	-
/4	240.0.0.0	268,435,456	268,435,454	-
/5	248.0.0.0	134,217,728	134,217,726	-
/6	252.0.0.0	67,108,864	67,108,862	-
/7	254.0.0.0	33,554,432	33,554,430	-
/8	255.0.0.0	16,777,216	16,777,214	-
/9	255.128.0.0	8,388,608	8,388,606	-
/10	255.192.0.0	4,194,304	4,194,302	-
/11	255.224.0.0	2,097,152	2,097,150	-
/12	255.240.0.0	1,048,576	1,048,574	-
/13	255.248.0.0	524,288	524,286	-
/14	255.252.0.0	262,144	262,142	-
/15	255.254.0.0	131,072	131,070	-
/16	255.255.0.0	65,536	65,534	-
/17	255.255.128.0	32,768	32,766	-
/18	255.255.192.0	16,384	16,382	-
/19	255.255.224.0	8,192	8,190	-
/20	255.255.240.0	4,096	4,094	-
/21	255.255.248.0	2,048	2,046	1
/22	255.255.252.0	1,024	1,022	2 split →
/23	255.255.254.0	512	510	4 split →
/24	255.255.255.0	256	254	8 split →
/25	255.255.255.128	128	126	16 split →
/26	255.255.255.192	64	62	32 split →
/27	255.255.255.224	32	30	64 split →
/28	255.255.255.240	16	14	128 split →
/29	255.255.255.248	8	6	256 split →
/30	255.255.255.252	4	2	512 split →
/31	255.255.255.254	2	2	1,024 split →
/32	255.255.255.255	1	1	2,048 split →

02 / faq

About this calculator.

How do I use this subnet calculator?

▼

Type an IP address followed by a prefix, like 192.168.1.10/24, or by a subnet mask, like 192.168.1.10 255.255.255.0. Without a prefix it uses /24. Click a row in the table to split the network into smaller subnets.

Why are usable hosts always 2 fewer?

▼

The first address in a subnet is the network address and the last is the broadcast address, so neither can go to a device. The exceptions are /31 (point-to-point links, RFC 3021) and /32 (a single address), which use every address.

Can I use it from a terminal?

▼

Yes. curl 'ipku.in/en/tools/ipv4-subnet-calculator?q=192.168.1.10/24' returns the result as plain text.

Learn how to work it out →