ANSI 6x6x6 Color Cube - How to Calculate Color Codes

The 6x6x6 Color Cube

Colors 16-231 in the 256-color palette form a 6x6x6 color cube. Understanding the math behind it lets you programmatically convert between RGB values and ANSI color codes.

The Formula

code = 16 + (36 * r) + (6 * g) + b

Where r, g, and b are indices from 0 to 5, representing these RGB values:

Index	RGB Value
0	0
1	95
2	135
3	175
4	215
5	255

Reverse Calculation

To find the RGB values from a color code:

# Python: Convert ANSI code to RGB
def ansi_to_rgb(code):
    code -= 16
    b = code % 6
    g = (code // 6) % 6
    r = code // 36
    values = [0, 95, 135, 175, 215, 255]
    return (values[r], values[g], values[b])

Finding the Nearest 256-Color

When you have an arbitrary RGB value, find the closest match:

def rgb_to_ansi256(r, g, b):
    values = [0, 95, 135, 175, 215, 255]
    ri = min(range(6), key=lambda i: abs(values[i] - r))
    gi = min(range(6), key=lambda i: abs(values[i] - g))
    bi = min(range(6), key=lambda i: abs(values[i] - b))
    return 16 + (36 * ri) + (6 * gi) + bi

Common Colors in the Cube

Color	Code	RGB
Pure Red	196	(255, 0, 0)
Pure Green	46	(0, 255, 0)
Pure Blue	21	(0, 0, 255)
Yellow	226	(255, 255, 0)
Cyan	51	(0, 255, 255)
Magenta	201	(255, 0, 255)
Orange	208	(255, 175, 0)
Pink	213	(255, 135, 255)

Practical Example

# Print a color gradient across the red axis
for r in 0 1 2 3 4 5; do
  code=$((16 + 36 * r))
  echo -en "\033[48;5;${code}m  \033[0m"
done
echo