The prefix length defines the boundary
A CIDR prefix such as /26 tells you how many leading address bits identify the network. IPv4 has 32 bits, so a /26 leaves 6 bits and contains 2⁶ = 64 addresses. A larger prefix number means a smaller range.
A calculator can normalize an address with host bits set. Entering 192.168.10.77/26 describes the subnet containing that address; it does not mean the subnet begins at .77.
Worked example: 192.168.10.77/26
A /26 has a mask of 255.255.255.192. Within this /24, its blocks start at .0, .64, .128, and .192. Address .77 belongs to the block beginning at .64 and ending at .127.
For an ordinary IPv4 subnet, 192.168.10.64 is the network address and 192.168.10.127 is the broadcast address. The conventional host range is .65–.126, giving 62 host addresses before any gateway, DHCP, or provider reservations.
- Network: 192.168.10.64/26
- Mask: 255.255.255.192
- Total addresses: 64
- Conventional usable host addresses: 62
- An address such as 192.168.10.128 is outside this subnet.
The exceptions matter
On an IPv4 point-to-point /31, both addresses can be endpoint addresses under RFC 3021. A /32 identifies one address. Subtracting two from every IPv4 range gives the wrong result for both cases.
IPv6 has 128 bits and no broadcast address. Do not subtract an IPv4-style network and broadcast pair from an IPv6 count. A range calculation describes address space; it does not determine what your router, provider, or application will permit you to assign.
Split, combine, and compare without adding extra space
Splitting 192.168.10.0/24 into /26 networks produces four equal blocks: .0/26, .64/26, .128/26, and .192/26. The splitter pages through the result instead of allocating a giant list; even an IPv6 /0 split into /128 entries remains a bounded calculation. Split exports contain the displayed page only.
For the range 192.168.1.10–192.168.1.20, the exact minimum cover is 192.168.1.10/31, 192.168.1.12/30, 192.168.1.16/30, and 192.168.1.20/32. A single larger subnet would include addresses outside that range. Range conversion avoids that overreach.
Aggregation removes duplicate or contained networks and merges adjacent blocks only when the resulting CIDR adds no addresses. For example, 192.168.1.0/25 plus 192.168.1.128/25 becomes 192.168.1.0/24. Separated networks remain separate. Membership and overlap checks help verify the exact result before applying it to a firewall or route list.
Use the result before changing a network
Check that the planned gateway and devices fall inside the intended range, compare it with existing local and VPN subnets, and keep any provider-reserved addresses out of your assignment plan. Overlapping private ranges can cause routing surprises when two networks are joined.
The subnet tool performs address arithmetic in your browser. It does not discover active devices, probe addresses, verify routes, or apply settings to your router.