Units, Numbers & Color
Convert units, number bases and color representations. Handy when checking CSS units or numbers in a screen design.
16 tools・Ordered by measured page views over the last 90 days.
Color Code Converter
Convert between HEX, RGB and HSL with a large live preview. Copy any notation in one click.
Number Base Converter
Convert between binary, octal, decimal and hex — accurate via BigInt.
Check Digit Calculator
Compute and verify the check digit for EAN-13/JAN, UPC-A, ISBN-13 and Luhn (credit cards). Enter a number and it validates the last digit too.
Kansuji Converter
Convert between Arabic numerals, Japanese kanji numerals, and formal daiji (壱弐参拾萬), including the money notation 金壱萬円也.
Contrast Ratio Checker
Check the contrast ratio between text and background colors and WCAG AA/AAA compliance. With color pickers and live preview.
Consumption Tax Calculator
Convert between tax-exclusive and tax-inclusive prices. Supports 10%, reduced 8% and custom rates.
Time Duration Calculator
Add and subtract HH:MM:SS durations across lines, with conversions to seconds, minutes, and hours.
Aspect Ratio Calculator
Find the aspect ratio (such as 16:9) from a width and height, or compute one dimension from a ratio and the other. Simplified with the greatest common divisor. Runs in your browser.
Roman Numeral Converter
Convert between Arabic numbers and Roman numerals (1-3999) with subtractive notation (IV, IX). Out-of-range or malformed input shows an error. Reference table included.
Percentage Calculator
What percent A is of B, A% of B, and the percent change from A to B — in three modes.
Data Size Unit Converter
Convert between B/KB/MB/GB (base 1000), KiB/MiB/GiB (base 1024), and bits. Understand storage vs OS display.
CSS Unit Converter
Convert px, rem, em, pt and % with configurable root and parent font sizes, so the rem/em difference is visible.
ISBN Converter (10 / 13)
Convert between ISBN-10 and ISBN-13 and verify the check digit. Shows the weights, sum and modulo so you can check the result by hand. Runs entirely in your browser.
Corporate Number Check Digit
Compute the check digit of a Japanese Corporate Number from its 12-digit body, or verify a full 13-digit number. Shows the odd and even digit sums. Runs in your browser.
Queue Simulator
Estimate wait time and utilisation from arrival rate, service time and server count, and compare server counts.
Work Hours Calculator
Total worked hours from clock-in, clock-out and breaks pasted one line per day, with 15-minute style rounding and overnight shifts.