Binary Converter
Binary is the language underneath subnetting: every mask, network address and host count is binary arithmetic. Type a value in any base and this converter shows decimal, binary, hexadecimal and octal side by side, with a bit grid that shows exactly which place values are switched on — the same binary the subnet calculator works with. Then test yourself in the practice box.
| Decimal | |
|---|---|
| Binary | |
| Hexadecimal | |
| Octal |
Practice: decimal to binary
Why binary fluency wins marks
The magic-number subnetting method works because each mask bit is a power of two. When you can read 10101000 as 128 + 32 + 8 = 168 without thinking, mask values like 255.255.255.192 stop being memorized facts and become obvious: 192 is 11000000, two bits borrowed, four subnets. Network+ tests number systems directly, and CCNA expects you to convert under time pressure.
Number systems show up on Network+ and CCNA — practice free
Try the free 30-question samples for Network+ N10-009 and CCNA 200-301 and see where you stand.
Free Network+ SampleFree CCNA SampleFAQ
How do you convert decimal to binary by hand?
Write out the place values 128, 64, 32, 16, 8, 4, 2, 1. Walk from left to right: if the value fits in your number, write a 1 and subtract it; if not, write a 0. For 168: 128 fits (1, remainder 40), 64 does not (0), 32 fits (1, remainder 8), 16 does not (0), 8 fits (1), then 0, 0, 0 — giving 10101000.
Why does the subnet mask 255.255.255.192 mean /26?
The last octet, 192, is 11000000 in binary — two bits are 1, and 24 + 2 = 26 network bits total, which is exactly what the /26 prefix counts. A /26 leaves 6 host bits, so 2^6 = 64 addresses per subnet.
What is hexadecimal used for in networking?
Hex appears in MAC addresses (written as hex pairs), IPv6 addresses (hex groups separated by colons), and many protocol fields and colour-style identifiers. Each hex digit is exactly 4 binary bits, which makes hex a compact way to write binary.
How does the practice mode work?
The practice box picks a random decimal number from 0 to 255 — one full octet, the range subnetting uses. Type its binary form and press Check for instant feedback, including the correct 8-bit answer with leading zeros.