tech calculator

IP & CIDR Range Calculator

Expand a CIDR block into its address range, masks, and host counts, then split it into equal subnets.

Network = IP AND Subnet Mask; Broadcast = Network OR Wildcard Mask; Usable Hosts = 2^(32 − prefix) − 2. Example: 192.168.1.0/24 has mask 255.255.255.0, wildcard 0.0.0.255, a range of 192.168.1.0–192.168.1.255, and 254 usable hosts. A /31 has 2 usable addresses under RFC 3021 and a /32 is a single host route.

Formula Verified by Dr. James Callahan, PhD

Quick actions: Save inputs, view saved runs, print, share, or export results

Saved Runs

Inputs

IPv4 Address

Prefix Length/

Split Into Subnets Of Prefix/

Results

CIDR Block

10.0.0.0/16

Address Range10.0.0.0 – 10.0.255.255

Network Address10.0.0.0

Broadcast Address10.0.255.255

First Usable Host10.0.0.1

Last Usable Host10.0.255.254

Subnet Mask255.255.0.0

Wildcard Mask (ACL syntax)0.0.255.255

Total Addresses65,536

Usable Hosts65,534

ScopePrivate (RFC 1918)

Legacy ClassA

Split into /24256 subnets of 256 addresses

First subnets10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24, 10.0.3.0/24, 10.0.4.0/24, 10.0.5.0/24, 10.0.6.0/24, 10.0.7.0/24 …

Tip

Keep it open while planning a VPC, writing a firewall rule, or checking which block a host address belongs to.

Formula

CIDR range formulas

Subnet Mask = 32 bits, the first (prefix) set to 1
Wildcard Mask = bitwise NOT of the subnet mask
Network Address = IP AND Subnet Mask
Broadcast Address = Network OR Wildcard Mask
Total Addresses = 2^(32 − prefix)
Usable Hosts = 2^(32 − prefix) − 2   (except /31 = 2 per RFC 3021, and /32 = 1)
Subnets when split into /n = 2^(n − parent prefix)

The prefix says how many leading bits identify the network; everything after it is host space. Because the network address is the IP masked down to those leading bits, any address inside a block resolves to the same block — enter 10.20.30.40/22 and you get 10.20.28.0/22 back, which is the correct answer and a common source of confusion. The two subtracted addresses are the network identifier and the broadcast address, neither of which can be assigned to a host.

Step by step

How the calculation works

1Enter any address inside the block and the prefix length. You do not need to enter the network address itself — the calculator masks whatever you give it down to the block it belongs to, which is usually what you want when you are checking where a specific host sits.
2The address range is the pair to paste into a firewall rule, security group, or allowlist. The wildcard mask is the same information in the inverted form Cisco ACLs and some routing configurations expect: 0.0.0.255 rather than 255.255.255.0.
3Usable hosts is two fewer than the total, because the first address identifies the network and the last is the broadcast address. Two prefixes are exceptions: a /31 has both addresses usable under RFC 3021 for point-to-point links, and a /32 is a single host route.
4The split field answers the planning question — how many /24 subnets fit inside this /16, and where does each one start? A /16 splits into 256 /24s or 16 /20s, and the calculator lists the first few boundaries so you can check your allocation lines up.
5Scope tells you whether the block is publicly routable or reserved: RFC 1918 private space, RFC 6598 carrier-grade NAT, loopback, link-local, or multicast. For dividing one block into differently sized subnets rather than equal ones, the [subnet calculator](/calculators/subnet-calculator) handles variable-length subnet masking.

Related guides

Learn more about this calculation

Guide

IPv4 Subnetting Basics: CIDR, Masks, and Hosts

Learn IPv4 subnetting with a clear /26 example: convert CIDR to a mask, find block boundaries, and calculate network, broadcast, and host ranges.

Guide

How to Use Do The Calculation Calculators: A Practical Step-by-Step Guide

Learn the fastest reliable workflow for using Do The Calculation calculators, reading results, checking formulas, and using save, print, share, and export actions correctly.

Tech Tool

Subnet Calculator

Plan variable-length subnet masking when the subnets you need are different sizes.

Guide

Subnetting Basics

CIDR notation, masks, and host counts explained from first principles.

Tech Tool

Binary, Hex & ASCII Converter

Convert an octet to binary when you want to see the mask boundary bit by bit.

Tech Tool

Bandwidth Calculator

Size the link serving the hosts you just allocated addresses for.

tech calculator

IP & CIDR Range Calculator

Expand a CIDR block into its address range, masks, and host counts, then split it into equal subnets.

Formula Verified by Dr. James Callahan, PhD

Quick actions: Save inputs, view saved runs, print, share, or export results

Saved Runs

Inputs

IPv4 Address

Prefix Length/

Split Into Subnets Of Prefix/

Results

CIDR Block

10.0.0.0/16

Address Range10.0.0.0 – 10.0.255.255

Network Address10.0.0.0

Broadcast Address10.0.255.255

First Usable Host10.0.0.1

Last Usable Host10.0.255.254

Subnet Mask255.255.0.0

Wildcard Mask (ACL syntax)0.0.255.255

Total Addresses65,536

Usable Hosts65,534

ScopePrivate (RFC 1918)

Legacy ClassA

Split into /24256 subnets of 256 addresses

First subnets10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24, 10.0.3.0/24, 10.0.4.0/24, 10.0.5.0/24, 10.0.6.0/24, 10.0.7.0/24 …

Tip

Keep it open while planning a VPC, writing a firewall rule, or checking which block a host address belongs to.

Summary

Key output metrics

Address Range

10.0.0.0 – 10.0.255.255

10.0.0.0/16

Usable Hosts

65,534

65,536 total addresses

Scope

Private (RFC 1918)

Legacy class A · mask 255.255.0.0

D3 visualization

Block Size by Prefix Length

Total addresses at each prefix around the one you entered. Every bit added to the prefix halves the block, which is why /24 and /16 boundaries feel so far apart.

Guide

How to understand and use this calculator

Quick Answer — How Do You Calculate a CIDR Range?

The prefix says how many leading bits identify the network. Everything else follows from masking: Network = IP AND Mask, Broadcast = Network OR Wildcard, Total Addresses = 2^(32-prefix), and Usable Hosts = 2^(32-prefix) - 2 — the two exceptions being a /31, where RFC 3021 makes both addresses usable on a point-to-point link, and a /32, which is a single host route.

Worked example: `192.168.1.0/24`. Mask 255.255.255.0, wildcard 0.0.0.255, network 192.168.1.0, broadcast 192.168.1.255, usable range 192.168.1.1 – 192.168.1.254, 256 total addresses and 254 usable hosts. Scope: private, RFC 1918.

Common prefixes at a glance:

/16 — mask 255.255.0.0, 65,536 addresses, 65,534 usable hosts
/20 — mask 255.255.240.0, 4,096 addresses, 4,094 usable hosts
/22 — mask 255.255.252.0, 1,024 addresses, 1,022 usable hosts
/24 — mask 255.255.255.0, 256 addresses, 254 usable hosts
/30 — mask 255.255.255.252, 4 addresses, 2 usable hosts
/31 — mask 255.255.255.254, 2 addresses, 2 usable (RFC 3021 point-to-point)
/32 — mask 255.255.255.255, 1 address, a single host route

Every bit added to the prefix halves the block. That is why /24 and /16 feel so far apart: eight bits of difference is a factor of 256.

How to Use This Calculator: Planning a VPC Address Range

Enter any address inside the block and the prefix. You do not have to enter the network address itself — the calculator masks whatever you give it down to the block that address belongs to.

Take `10.0.0.0/16`, a common private VPC allocation. Mask 255.255.0.0, wildcard 0.0.255.255, range 10.0.0.0 – 10.0.255.255, first usable 10.0.0.1, last usable 10.0.255.254, 65,536 addresses and 65,534 usable hosts, scope private (RFC 1918).

Now split it. Set the child prefix to /24 and the block divides into 256 subnets of 256 addresses each, starting 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24, 10.0.3.0/24 and continuing. Set it to /20 instead and you get 16 subnets of 4,096 addresses, starting 10.0.0.0/20, 10.0.16.0/20, 10.0.32.0/20, 10.0.48.0/20.

The boundaries are the part worth checking. A /20 does not start every 20 addresses or every 20 anything — it starts every 4,096 addresses, which lands on the third octet in steps of 16. Getting that wrong is how overlapping subnets end up in a routing table.

A Second Example: Where Does This Host Actually Live?

The other everyday question is the reverse — you have a host address and a prefix, and you need the block. Enter `10.20.30.40/22`:

The calculator returns 10.20.28.0/22, not 10.20.30.0/22. Masking 10.20.30.40 with 255.255.252.0 clears the low two bits of the third octet, and 30 in binary is 00011110, which masks down to 00011100 — 28. So the block runs 10.20.28.0 – 10.20.31.255, usable 10.20.28.1 – 10.20.31.254, 1,024 addresses and 1,022 usable hosts.

This surprises people regularly, and it is the correct answer rather than a quirk: `10.20.30.40/22` and `10.20.28.0/22` describe the identical block. It matters because a firewall rule written against the address you happened to have in hand covers three other /24s you may not have intended to include.

Two more edge cases worth knowing. `203.0.113.5/31` returns 203.0.113.4 – 203.0.113.5 with both addresses usable — RFC 3021 dispensed with the network and broadcast reservation on point-to-point links, which is why /31 is standard on router-to-router links today. And `203.0.113.5/32` is a single address, the form used for host routes and single-IP allowlist entries.

Subnet Mask, Wildcard Mask, and How This Differs From VLSM

A subnet mask and a wildcard mask carry the same information inverted. The subnet mask sets the network bits to 1 (255.255.255.0 for a /24); the wildcard mask sets the host bits to 1 instead (0.0.0.255). Cisco access control lists and several routing protocols expect the wildcard form, so having both side by side saves a conversion step that is easy to get backwards under pressure.

Scope classification matters more than the legacy address class does. RFC 1918 private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are not routable on the public internet; RFC 6598 shared space (100.64.0.0/10) is carrier-grade NAT and will collide with your addressing if a provider uses it upstream. The old A/B/C classes are shown for reference, but classful addressing has not governed routing since CIDR replaced it — a /22 does not belong to any class in any operational sense.

This calculator handles a block and equal-sized children. When the subnets you need are deliberately *different* sizes — a 500-host site, a 60-host branch, and a handful of point-to-point links carved from one allocation — that is variable-length subnet masking, and the subnet calculator plans it. Use this one for range expansion and clean binary splits; use that one when the allocation is uneven. For the underlying theory, the subnetting basics guide works through CIDR notation, masks, and host counts from first principles.

Limitations

This calculator is IPv4 only. IPv6 uses the same CIDR prefix idea with a 128-bit address space, but the arithmetic, the notation, and the conventions differ enough that applying these results to an IPv6 plan will mislead you — a /64 is the standard IPv6 subnet and contains more addresses than the entire IPv4 space.

It describes addressing, not reachability. A block being private, correctly masked, and correctly split says nothing about whether traffic actually flows: routing tables, NAT, security group rules, and overlapping allocations elsewhere in your network all decide that. It also cannot tell you whether a range is already in use — the most common real-world CIDR failure is not bad arithmetic but allocating a block that collides with a VPN peer, a partner network, or a default range on some appliance.

The usable-host count assumes conventional host addressing. Some equipment can be configured to use the all-zeros or all-ones address in a subnet, and cloud providers reserve additional addresses inside every subnet you create — typically three to five per block for the gateway, DNS, and future use — so a /24 in a public cloud usually yields fewer than 254 assignable addresses. Check your provider's documentation before sizing a subnet to the exact number of hosts you need.

Related Calculators

For allocations where the subnets are deliberately different sizes, the Subnet Calculator plans variable-length subnet masking rather than equal binary splits. The Subnetting Basics guide covers CIDR notation, masks, and host counts from first principles if you want the theory behind these numbers. When you want to see a mask boundary bit by bit, the Binary, Hex ASCII Converter converts an octet directly, and once the addressing is settled the Bandwidth Calculator sizes the link serving those hosts.

Related concepts

CIDR Notation

An address plus a prefix length, as in 10.0.0.0/16. The prefix counts the leading bits that identify the network; the remainder is host space.

Wildcard Mask

The bitwise inverse of a subnet mask, with host bits set to 1. The form Cisco ACLs and several routing protocols expect — 0.0.0.255 rather than 255.255.255.0.

RFC 3021 /31 Links

A convention that drops the network and broadcast reservation on point-to-point links, making both addresses in a /31 assignable and halving the waste of the older /30 approach.

Frequently Asked Questions

How do I calculate the IP range of a CIDR block?+

AND the address with the subnet mask to get the network address, then OR that with the wildcard mask to get the broadcast address — those two are the range. For 192.168.1.0/24 the range is 192.168.1.0 to 192.168.1.255, with 192.168.1.1 to 192.168.1.254 assignable to hosts.

How many usable hosts are in a /24?+

254. A /24 contains 2^(32−24) = 256 addresses, minus the network address and the broadcast address, neither of which can be assigned to a host. The same rule gives 1,022 for a /22, 4,094 for a /20, and 65,534 for a /16.

Why does 10.20.30.40/22 come back as 10.20.28.0/22?+

Because they are the same block. A /22 mask clears the low two bits of the third octet, and 30 masks down to 28, so 10.20.30.40 sits inside the block 10.20.28.0/22 which runs from 10.20.28.0 to 10.20.31.255. Any address inside a block resolves to that block's network address.

What is the difference between a subnet mask and a wildcard mask?+

They are bitwise inverses carrying the same information. A subnet mask sets the network bits to 1 — 255.255.255.0 for a /24 — while a wildcard mask sets the host bits to 1 instead, giving 0.0.0.255. Cisco access control lists and some routing protocols use the wildcard form.

Why does a /31 have two usable hosts instead of zero?+

RFC 3021 removed the network and broadcast reservation for point-to-point links, where there is no broadcast domain to identify. That makes both addresses in a /31 assignable, which is why /31 rather than /30 is now standard on router-to-router links — it halves the address waste.

How many /24 subnets fit in a /16?+

256, each containing 256 addresses. The general rule is 2^(child prefix − parent prefix), so a /16 gives 16 /20s, 256 /24s, or 1,024 /26s. Set the split field to see the actual starting boundaries, which is where allocations usually go wrong.

Which IP ranges are private?+

The RFC 1918 ranges 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are private and not routable on the public internet. 100.64.0.0/10 is RFC 6598 shared space used for carrier-grade NAT, 127.0.0.0/8 is loopback, and 169.254.0.0/16 is link-local. The calculator labels whichever applies.

Will a /24 give me 254 addresses in a cloud VPC?+

Usually not. Cloud providers reserve extra addresses inside every subnet — commonly three to five for the gateway, DNS resolver, and future use — on top of the network and broadcast addresses. Check your provider's documentation before sizing a subnet to the exact host count you need.

Formula

CIDR range formulas

Subnet Mask = 32 bits, the first (prefix) set to 1
Wildcard Mask = bitwise NOT of the subnet mask
Network Address = IP AND Subnet Mask
Broadcast Address = Network OR Wildcard Mask
Total Addresses = 2^(32 − prefix)
Usable Hosts = 2^(32 − prefix) − 2   (except /31 = 2 per RFC 3021, and /32 = 1)
Subnets when split into /n = 2^(n − parent prefix)

Step by step

How the calculation works

1Enter any address inside the block and the prefix length. You do not need to enter the network address itself — the calculator masks whatever you give it down to the block it belongs to, which is usually what you want when you are checking where a specific host sits.
2The address range is the pair to paste into a firewall rule, security group, or allowlist. The wildcard mask is the same information in the inverted form Cisco ACLs and some routing configurations expect: 0.0.0.255 rather than 255.255.255.0.
3Usable hosts is two fewer than the total, because the first address identifies the network and the last is the broadcast address. Two prefixes are exceptions: a /31 has both addresses usable under RFC 3021 for point-to-point links, and a /32 is a single host route.
4The split field answers the planning question — how many /24 subnets fit inside this /16, and where does each one start? A /16 splits into 256 /24s or 16 /20s, and the calculator lists the first few boundaries so you can check your allocation lines up.
5Scope tells you whether the block is publicly routable or reserved: RFC 1918 private space, RFC 6598 carrier-grade NAT, loopback, link-local, or multicast. For dividing one block into differently sized subnets rather than equal ones, the [subnet calculator](/calculators/subnet-calculator) handles variable-length subnet masking.

Related guides

Learn more about this calculation

Guide