HEX color contrast ratio

Calculate hex color contrast ratio using the values and assumptions you provide.

Your inputs stay in your browser. Displayed results are rounded to a maximum of 12 significant digits.

Method and assumptions

Method version 1.0.0 · Updated October 18, 2026

Calculate

Formula: (L_lighter + 0.05) / (L_darker + 0.05), sRGB luminance

Calculate hex color contrast ratio using the values and assumptions you provide.

color1: Text color (#HEX)
color2: Background color (#HEX)

Results depend on the assumptions entered; verify professional or safety-critical decisions independently.

Calculate with code

These short examples use the same inputs and core calculation as this tool. Adapt validation and formatting to your application.

JavaScript

const luminance = rgb => rgb.map(c => c <= .04045 ? c/12.92 : ((c+.055)/1.055)**2.4).reduce((s,c,i)=>s+c*[.2126,.7152,.0722][i],0);
const ratio = (1 + .05) / (luminance([0,0,0]) + .05);
console.log(ratio); // 21 for black on white

TypeScript

const luminance = (rgb: number[]) => rgb.map(c => c <= .04045 ? c/12.92 : ((c+.055)/1.055)**2.4).reduce((s,c,i)=>s+c*[.2126,.7152,.0722][i]!,0);
console.log((1.05)/(luminance([0,0,0])+.05)); // 21

Python

def lum(rgb):
    c = [v/12.92 if v <= .04045 else ((v+.055)/1.055)**2.4 for v in rgb]
    return sum(x*w for x,w in zip(c, (.2126,.7152,.0722)))
print(1.05 / (lum((0,0,0)) + .05))  # 21:1 black/white

Java

double black = 0, white = 1;
System.out.println((white + .05) / (black + .05)); // 21:1 (black/white)

double black = 0, white = 1;
Console.WriteLine((white + .05) / (black + .05)); // 21:1 black/white