Binary clock
A live binary clock that shows your local time in lights. Pick the BCD style, with one column per digit, or true binary, with one row each for hours, minutes and seconds. Turn on the numbers while you learn, then hide them and read the lights alone.
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How to read a binary clock
In the BCD style, short for binary-coded decimal, there are six columns: two for hours, two for minutes and two for seconds. Each column is one digit of the time. The lights in a column are worth 8, 4, 2 and 1 from top to bottom. Add the values of the lit lights to get the digit.
- Read the first column (tens of hours). It only needs 2 lights because it never goes above 2.
- Read the second column (ones of hours). Lights for 4 and 2 make 6, for example.
- Do the same for the minute and second columns. The tens columns only need 3 lights because they never go above 5.
- Put the digits together as HH:MM:SS.
Example: if the columns read 1, 4, 3, 5, 0 and 9, the time is 14:35:09.
| Column | Digit | Lit lights | Bits |
|---|---|---|---|
| Hours, tens | 1 | 1 | 01 |
| Hours, ones | 4 | 4 | 0100 |
| Minutes, tens | 3 | 2 + 1 | 011 |
| Minutes, ones | 5 | 4 + 1 | 0101 |
| Seconds, tens | 0 | none | 000 |
| Seconds, ones | 9 | 8 + 1 | 1001 |
True binary style
Switch Style to True binary and each unit gets one row holding the whole number. Hours use 5 lights (16, 8, 4, 2, 1), and minutes and seconds use 6 (32, 16, 8, 4, 2, 1). So 35 minutes is 100011: 32 + 2 + 1, the same answer the decimal to binary converter gives for 35. It is harder to read at a glance but closer to how a computer stores the number.
Options
- 12-hour shows 1 to 12 with AM or PM in the readout.
- Seconds can be turned off for a calmer clock with four columns.
- Show numbers puts the decimal digit under each column. Turn it off to test yourself.
- Show a time freezes the clock on any time you type, such as 07:42, so you can practice. Press Live to go back.
- Full screen turns the page into a desk or wall clock.
Practice
Set a time with "Show a time", hide the numbers, and read it back. Start with times where every digit is 1, 2, 4 or 8, since only one light is on. Then try digits like 3, 5, 6 and 7 that need two or three lights. To check a reading in the true binary style, the binary numbers chart lists every value from 0 to 1023. Most people can read a BCD clock without counting after a day or two.
Frequently asked questions
What time zone does the clock use?
The time from your device, so it matches the clock on your computer or phone.
Why does the first column have only two lights?
The tens digit of the hour is at most 2, which needs only the 2 and 1 lights.
What is the difference between BCD and true binary clocks?
BCD shows each decimal digit in its own column. True binary shows the whole hour, minute and second as one binary number each.
Can I use it as a screensaver?
Press Full screen and leave the tab open. The clock keeps time while the page is visible.