Binary Clock — Read the Time in Binary

A binary clock shows the time using columns of lit and unlit dots instead of digits. This one uses BCD (binary-coded decimal): six columns for the two digits each of hours, minutes and seconds. A decimal readout underneath shows the same time in normal numbers so you can check your reading as you learn.

How to read a BCD binary clock

Each column encodes one decimal digit. Reading top-to-bottom, the dots are worth 8, 4, 2 and 1; add up the lit dots in a column to get that digit. The two left columns are the hour, the middle two are minutes, and the right two are seconds. With a little practice you'll read it at a glance.

Guides about Binary Clock

Clocks for programmers Binary, Analog, and Digital Clocks Compared A clear comparison of binary, analog, and digital clocks, covering how each encodes the time, what they teach, how easy they are to read, and when to choose each. 6 min read Binary & BCD explained Binary Clock vs BCD Clock: What's the Difference? A side-by-side comparison of true binary clocks and BCD clocks, explaining how each encodes the time, how to tell them apart, and how to read both with worked examples. 6 min read Learning binary numbers Binary Numbers Explained: Base Two Made Simple A from-scratch explanation of binary numbers: how base two works, why each place value doubles, and how to read and write ones and zeros, with worked examples. 6 min read Learning binary numbers How to Convert Decimal to Binary (Step by Step) A step-by-step guide to converting decimal numbers into binary using two reliable methods, with worked examples and tips for practising on a live binary clock. 6 min read Binary clock history The History of Binary Clocks and Binary Numbers A tour through the history of binary clocks and the binary system itself, from Leibniz's seventeenth-century breakthrough to the LED novelty timepieces of today. 5 min read Reading a binary clock How to Read a Binary Clock: A Beginner's Guide A friendly step-by-step guide to reading a binary clock, explaining the 8-4-2-1 dot values, how each column of lights encodes a digit, and how to decode the full time. 6 min read

More binclock pages

Digital Clock A plain 24-hour digital clock for comparison with the binary display. Analog Clock A classic analog clock face showing the current time.

Frequently asked questions

What does BCD mean?

Binary-coded decimal — each decimal digit of the time (0–9) is shown as a 4-bit binary number in its own column, which is easier to read than pure binary.

How do I read it?

In each column the dots are worth 8, 4, 2 and 1 from top to bottom; add the lit ones to get the digit. Columns are HH:MM:SS left to right.

Is there a decimal readout?

Yes — the normal digital time is shown under the dots so you can check yourself while learning.