A binary clock displays the current time using binary digits (bits) instead of decimal numerals. Each lit LED represents a binary 1; unlit LEDs represent 0. Our clock uses BCD (Binary-Coded Decimal) encoding — the most common format — where each decimal digit of the time is independently encoded in 4‑bit binary.

The clock has 6 columns grouped into pairs: Hours (HH), Minutes (MM), and Seconds (SS). Each column has 4 LEDs representing weights 8, 4, 2, 1 from top to bottom. To get the digit value, sum the weights of all lit LEDs in that column. For example, if the 4‑LED and 1‑LED are lit, the digit is 4+1 = 5. Read left to right: H₁H₀ : M₁M₀ : S₁S₀.

BCD is a method of encoding decimal numbers where each individual digit (0–9) is represented by its own 4‑bit binary sequence. This differs from pure binary, where the entire number is converted as a whole. BCD makes it easier to read clock digits directly, which is why most binary clocks — including classic models like the ThinkGeek Binary Clock — use this format.

The hour tens column (H₁) only needs values 0, 1, or 2, so the 8‑bit and 4‑bit are never used there. Similarly, the minute and second tens columns only go up to 5, so the 8‑bit is never lit. This is normal and reflects the valid range of each digit in a 24‑hour clock.

Yes! Click the 24H/12H toggle button above the clock. In 12‑hour mode, hours are converted to the 1–12 range (with AM/PM indicator shown in the digital display). The BCD columns update accordingly. The 24‑hour format is the default and the most traditional for binary clocks.

This clock runs off your device's local system time, which is typically synced via NTP (Network Time Protocol) automatically by your operating system. It updates every second in real time with sub‑second precision. There is no manual calibration needed.

We offer five themes: Neon Green (classic retro-computer aesthetic), Cyber Blue (cool modern tech), Amber Glow (warm vintage terminal), Rose Red (vibrant & bold), and Clean White (minimalist). Click any color dot above the clock to switch themes. Your preference is saved in your browser.