CIDR Range Calculator
Work out the address range, count and boundaries of a CIDR block.
Reading a CIDR block
CIDR notation writes an IP range compactly as an address and a prefix length, like 10.0.0.0/24. This works out what that block actually covers — the first and last address, how many addresses it contains, and the range boundaries — so you can plan or verify network allocations without doing the binary maths by hand.
Enter a CIDR block and its range is calculated.
Why the prefix is everything
The number after the slash is the whole story: it says how many bits are fixed, and therefore how large the block is. Each step in the prefix halves or doubles the size, so /24 holds two hundred and fifty-six addresses and /23 twice that. This is the daily arithmetic of allocating address space — carving a range into right-sized blocks without overlaps or waste. Seeing the exact addresses a CIDR covers is what lets you check that two blocks do not collide and that each fits the number of hosts it needs to.
Questions & answers
What does the prefix like /24 control?
How many bits are fixed as the network portion, which sets the block's size — a smaller prefix number means a larger range.
What does the calculator show?
The first and last address, the total count, and the boundaries of the CIDR block.
Is anything uploaded?
No. The calculation happens in your browser.