holpxay n. [hol.ˈp’aj] number.

A notepad calculator where math just works. Type expressions, see results instantly.

Features

Arithmetic & Numbers

• Basic math with +, -, *, /, ^, !, mod, and parentheses
• Alternative operators: ×, ·, ÷
• Percentages (50%, 200 * 15%), scientific notation, underscore separators
• Hex (0xFF), binary (0b1010), octal (0o777), arbitrary bases (ABC base 16)
• Built-in constants (pi, e, phi) and functions (sin, cos, sqrt, log, round, abs, random, …)

Units & Conversions

• 200+ built-in units across length, mass, time, temperature, data, energy, power, pressure, frequency, angle, and more
• Automatic cross-unit arithmetic: 5 km + 500 m, 100 ft^2 + 5 m^2
• Derived units: 60 km/h, 9.8 m/s^2, 50 watts per square meter
• Composite values: 5 ft 7 in, 2 hr 30 min 15 sec
• Flexible conversion syntax: to, in, as, ->, →
• Composite conversion targets: 171 cm to ft in
• User-defined units: 150 apples / 30 apples/day

Date & Time

• Date literals, relative dates (today, 3 days ago, 2 weeks from now)
• Time values in 12h/24h format
• Date arithmetic: now + 100 days, 2038 Jan 19 - today
• Timezone conversions: 18:30 Tokyo, now in London, UTC offsets
• Unix timestamps: 1700000000 unix
• Property extraction: today to weekday, now to hour

Currency

• ISO codes, symbols, and names with live exchange rates
• Arithmetic and conversion: 100 USD + 50 EUR, 100 USD to JPY
• Derived currency units: 150 USD/person * 4 person

Variables & Conditionals

• Variable assignment: price = 49.99
• Boolean expressions: comparisons, &&, ||, !
• Conditionals: if 5 > 3 then 100 else 200
• Bitwise operations: &, |, xor, ~, <<, >>

Output Formats

• Number bases (to hex, to binary), fractions, scientific notation, percentages, ordinals
• Precision control: pi to 2 decimals, 12345 to 3 sig figs
• Date/time formats: ISO 8601, RFC 2822, RFC 9557, unix timestamps

Editor

• Markdown headings and inline comments (#)
• GFM syntax highlighting alongside live calculations
• Customizable themes, fonts, number/date formatting, and more