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)10.0.16.0/21

network10.0.16.0/21

broadcast10.0.23.255

first host10.0.16.1

last host10.0.23.254

subnet mask255.255.248.0

wildcard0.0.7.255

addresses2,048

usable hosts2,046

classA

ipcalc 10.0.16.0/21

address00001010.00000000.00010000.00000000

subnet mask11111111.11111111.11111000.00000000

network00001010.00000000.00010000.00000000

broadcast00001010.00000000.00010111.11111111

green = network part, grey = host part

hex0x0a001000

decimal167776256

reverse dns0.16.0.10.in-addr.arpa

ipv4-mapped::ffff:a00:1000

/21 split into /27 · 64 subnets

close ×

#	network	host range	broadcast
1	10.0.16.0/27	10.0.16.1 – 10.0.16.30	10.0.16.31
2	10.0.16.32/27	10.0.16.33 – 10.0.16.62	10.0.16.63
3	10.0.16.64/27	10.0.16.65 – 10.0.16.94	10.0.16.95
4	10.0.16.96/27	10.0.16.97 – 10.0.16.126	10.0.16.127
5	10.0.16.128/27	10.0.16.129 – 10.0.16.158	10.0.16.159
6	10.0.16.160/27	10.0.16.161 – 10.0.16.190	10.0.16.191
7	10.0.16.192/27	10.0.16.193 – 10.0.16.222	10.0.16.223
8	10.0.16.224/27	10.0.16.225 – 10.0.16.254	10.0.16.255
9	10.0.17.0/27	10.0.17.1 – 10.0.17.30	10.0.17.31
10	10.0.17.32/27	10.0.17.33 – 10.0.17.62	10.0.17.63
11	10.0.17.64/27	10.0.17.65 – 10.0.17.94	10.0.17.95
12	10.0.17.96/27	10.0.17.97 – 10.0.17.126	10.0.17.127
13	10.0.17.128/27	10.0.17.129 – 10.0.17.158	10.0.17.159
14	10.0.17.160/27	10.0.17.161 – 10.0.17.190	10.0.17.191
15	10.0.17.192/27	10.0.17.193 – 10.0.17.222	10.0.17.223
16	10.0.17.224/27	10.0.17.225 – 10.0.17.254	10.0.17.255
17	10.0.18.0/27	10.0.18.1 – 10.0.18.30	10.0.18.31
18	10.0.18.32/27	10.0.18.33 – 10.0.18.62	10.0.18.63
19	10.0.18.64/27	10.0.18.65 – 10.0.18.94	10.0.18.95
20	10.0.18.96/27	10.0.18.97 – 10.0.18.126	10.0.18.127
21	10.0.18.128/27	10.0.18.129 – 10.0.18.158	10.0.18.159
22	10.0.18.160/27	10.0.18.161 – 10.0.18.190	10.0.18.191
23	10.0.18.192/27	10.0.18.193 – 10.0.18.222	10.0.18.223
24	10.0.18.224/27	10.0.18.225 – 10.0.18.254	10.0.18.255
25	10.0.19.0/27	10.0.19.1 – 10.0.19.30	10.0.19.31
26	10.0.19.32/27	10.0.19.33 – 10.0.19.62	10.0.19.63
27	10.0.19.64/27	10.0.19.65 – 10.0.19.94	10.0.19.95
28	10.0.19.96/27	10.0.19.97 – 10.0.19.126	10.0.19.127
29	10.0.19.128/27	10.0.19.129 – 10.0.19.158	10.0.19.159
30	10.0.19.160/27	10.0.19.161 – 10.0.19.190	10.0.19.191
31	10.0.19.192/27	10.0.19.193 – 10.0.19.222	10.0.19.223
32	10.0.19.224/27	10.0.19.225 – 10.0.19.254	10.0.19.255
33	10.0.20.0/27	10.0.20.1 – 10.0.20.30	10.0.20.31
34	10.0.20.32/27	10.0.20.33 – 10.0.20.62	10.0.20.63
35	10.0.20.64/27	10.0.20.65 – 10.0.20.94	10.0.20.95
36	10.0.20.96/27	10.0.20.97 – 10.0.20.126	10.0.20.127
37	10.0.20.128/27	10.0.20.129 – 10.0.20.158	10.0.20.159
38	10.0.20.160/27	10.0.20.161 – 10.0.20.190	10.0.20.191
39	10.0.20.192/27	10.0.20.193 – 10.0.20.222	10.0.20.223
40	10.0.20.224/27	10.0.20.225 – 10.0.20.254	10.0.20.255
41	10.0.21.0/27	10.0.21.1 – 10.0.21.30	10.0.21.31
42	10.0.21.32/27	10.0.21.33 – 10.0.21.62	10.0.21.63
43	10.0.21.64/27	10.0.21.65 – 10.0.21.94	10.0.21.95
44	10.0.21.96/27	10.0.21.97 – 10.0.21.126	10.0.21.127
45	10.0.21.128/27	10.0.21.129 – 10.0.21.158	10.0.21.159
46	10.0.21.160/27	10.0.21.161 – 10.0.21.190	10.0.21.191
47	10.0.21.192/27	10.0.21.193 – 10.0.21.222	10.0.21.223
48	10.0.21.224/27	10.0.21.225 – 10.0.21.254	10.0.21.255
49	10.0.22.0/27	10.0.22.1 – 10.0.22.30	10.0.22.31
50	10.0.22.32/27	10.0.22.33 – 10.0.22.62	10.0.22.63
51	10.0.22.64/27	10.0.22.65 – 10.0.22.94	10.0.22.95
52	10.0.22.96/27	10.0.22.97 – 10.0.22.126	10.0.22.127
53	10.0.22.128/27	10.0.22.129 – 10.0.22.158	10.0.22.159
54	10.0.22.160/27	10.0.22.161 – 10.0.22.190	10.0.22.191
55	10.0.22.192/27	10.0.22.193 – 10.0.22.222	10.0.22.223
56	10.0.22.224/27	10.0.22.225 – 10.0.22.254	10.0.22.255
57	10.0.23.0/27	10.0.23.1 – 10.0.23.30	10.0.23.31
58	10.0.23.32/27	10.0.23.33 – 10.0.23.62	10.0.23.63
59	10.0.23.64/27	10.0.23.65 – 10.0.23.94	10.0.23.95
60	10.0.23.96/27	10.0.23.97 – 10.0.23.126	10.0.23.127
61	10.0.23.128/27	10.0.23.129 – 10.0.23.158	10.0.23.159
62	10.0.23.160/27	10.0.23.161 – 10.0.23.190	10.0.23.191
63	10.0.23.192/27	10.0.23.193 – 10.0.23.222	10.0.23.223
64	10.0.23.224/27	10.0.23.225 – 10.0.23.254	10.0.23.255

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 →