How to Read a Binary Clock

Two Methods:BCD (Binary Coded Decimal) ModeTrue Binary Mode

Impress your friends by putting a binary clock on your desk. You can read it in two modes using these simple steps.

The idea of the binary clock is simple. Instead of displaying numbers in base 10 (which most people are used to), it uses binary (base 2) which only uses 1s and 0s. Because there are only two digits, lights can be used in place of the digits. "On" signifies a 1 and "Off" means 0. Reading the clock is only a matter of converting the binary value to decimal.

Method 1
BCD (Binary Coded Decimal) Mode

  1. Image titled Read a Binary Clock Step 1
    Decode each binary digit. The clock is divided into three sections, each containing two columns of lights. The first section displays hours, the second minutes, and the final section tells the seconds. The first column in each section represents the first digit (10's place) and the second column displays the second digit (or 1's place). Each column is composed of 2-4 lights, each representing a power of two. Starting at the bottom, the first light represents 20 (1), the second represents 21 (2), the third is 22 (4), and the top light represents 23 (8). In the picture, you can easily see this by the numbers to the left of each row. Add the corresponding values of every light in the column that is lit to find the appropriate number. For example, if the bottom three lights are lit, the number is 4 (third row) + 2 (second row) + 1 (bottom row) = 7. (See the second digit of the minutes in the picture.)
  2. Image titled Read a Binary Clock Step 2
    Read the hour by decoding the first section. In the picture, the bottom light (first row represents 1) in the first column is lit and the second column is blank (0). Combining the digits, you get 10 o'clock.
    NOTE: the time is displayed in 24hr time. Subtract 12 from the number if it is 13 or greater. For example, 15 would be 3 o'clock.
  3. Image titled Read a Binary Clock Step 3
    Find the minutes using the same process as before. Again looking at the picture; in the middle section, the first two (bottom) lights in the first column are lit (second row represents 2 and the first row is 1; 2 + 1 = 3) and the first three in the second column are lit (third row represents 4, second 2, and first 1; 4 + 2 + 1 = 7), combining the two digits, we find it is 37 minutes past the hour.
  4. Image titled Read a Binary Clock Step 4
    Decode the seconds. This can sometimes be tricky on an active clock because the seconds are ever changing. In the picture, the third light in the first column (third row represents 4) and the fourth and first light in the second column (fourth row is 8 and first is 1; 8 + 1 = 9) are lit, displaying 49 seconds. If you forget what number a light stands for, look at the number directly to the left of the row.
  5. Image titled Read a Binary Clock Step 5
    Combine the numbers to read the time.

Method 2
True Binary Mode

  1. Image titled Read a Binary Clock Step 6
    Decode each binary digit the same way as in BCD mode, but the two columns in each section now act as a single column. The lights in the right column still represent 20, 21, 22, and 23 respectively, but the left column continues the pattern. Starting from the bottom, the first light represents 24 (16) and the second 25 (32). There is no need to continue past 25 because 59 (the highest number needed) can be written as 111011 (25 + 24 + 23 + 21 + 20 = 32 + 16 + 8 + 2 + 1 = 59).
    Remember: the clock uses lights instead of digits; on is 1 and off is 0.
  2. Image titled Read a Binary Clock Step 7
    Read the hours. Using the watch as an example, the last two lights, on the top row, are lit (2 + 1 = 3), so it is 3 o'clock. Note that the LEDs on the watch are arranged in rows. The lights may be arranged in columns or rows, but reading it is the same. Remember on is 1 and off is 0. The hours on the watch can be written in binary as 0011 which is 3 in decimal.
  3. Image titled Read a Binary Clock Step 8
    Find the minutes. Again looking at the watch, we have 011001, on the bottom row, which corresponds to 24 + 23 + 20 = 16 + 8 + 1 = 25 minutes.
  4. Image titled Read a Binary Clock Step 9
    Decode the seconds the same way as hours and minutes. The watch in the picture does not display seconds.


  • Practice makes perfect! Binary clocks are very hard to read so just practice, practice, practice!
  • Don't dwell on the math. All you need to do is remember what value each light represents.
  • To improve your ability to memorize the combinations of lights, you can watch the seconds column and count along with it. This gets you familiar with the light combinations, and will make reading the time easier and quicker.
  • Sometimes the columns may be arranged horizontally (like the watch above). The procedure to decode the time is still the same.


  • If you want to show off in front of your friends, make sure you can read binary with ease. All they have to do is look at a regular clock to determine if you are wrong. And won't that be bad!

Things You'll Need

  • Binary clock or watch

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