Number & Date Tools

Free online number and date tools - age calculator, unit converter, percentage calculator, Unix timestamp converter, color converter.

Free Number & Date Tools - Instant Calculations Online

These five number and date tools handle the everyday calculations and conversions that come up in daily life, travel, finance, and software development. All tools run entirely in your browser - calculations are instant, no data is sent to any server, and the tools work offline once the page has loaded. No account required, completely free to use without limits.

Age Calculator

The Age Calculator computes an exact age in years, months, and days from a date of birth to today (or to any other target date). Unlike simple subtraction of years, the calculator correctly handles month and day differences - so if today is March 15 and your birthday is September 20, it correctly shows 6 months and 25 days remaining until the next birthday rather than treating the current year as a completed year. Additional outputs include the next birthday date, the day of the week you were born, the total number of days you have lived, and your age in months. Useful for verifying ages for official documents, calculating age eligibility for events, or just satisfying curiosity about exactly how many days old you are.

Unit Converter

The Unit Converter converts between metric and imperial measurements across all major measurement categories: Length (millimetres, centimetres, metres, kilometres, inches, feet, yards, miles, nautical miles), Weight/Mass (milligrams, grams, kilograms, tonnes, ounces, pounds, stone, short tons), Temperature (Celsius, Fahrenheit, Kelvin), Volume (millilitres, litres, fluid ounces, cups, pints, quarts, gallons - both US and UK), Area (square centimetres, square metres, square kilometres, square inches, square feet, acres, hectares), and Speed (metres per second, km/h, mph, knots). All conversions use exact SI-defined conversion factors for maximum precision. Temperature uses the correct offset formulas (not just multiplication) so Celsius to Fahrenheit conversions are always accurate.

Percentage Calculator

The Percentage Calculator handles all four common percentage calculation types. "What is X% of Y?" - for finding a sale discount amount, calculating tax, or working out a commission (e.g., what is 15% of £280?). "X is what percentage of Y?" - for expressing a score as a percentage or finding a market share (e.g., 42 out of 60 is what percent?). "Percentage change from X to Y" - for calculating growth rates, price changes, or performance improvements (e.g., from £80 to £96 is what percentage increase?). "Apply X% increase/decrease to Y" - for calculating a price after a discount or markup (e.g., £150 with a 20% discount = ?). Each calculation type shows the formula used alongside the result so you can verify and understand the method.

Unix Timestamp Converter

Unix timestamps are integers representing the number of seconds (or milliseconds) elapsed since January 1, 1970 00:00:00 UTC - the universal time standard for computer systems. They appear in API responses, database records, log files, JWT authentication tokens, and event tracking systems. The Timestamp Converter translates a Unix timestamp to a human-readable date and time displayed in your local timezone, in UTC, and in ISO 8601 format. The reverse operation - entering a date and time to get the corresponding Unix timestamp - is useful for constructing date range queries for APIs or databases. The converter auto-detects whether a timestamp is in seconds (10 digits) or milliseconds (13 digits, as used by JavaScript's Date.now()).

Color Converter

Colors in web design and digital work are expressed in multiple formats depending on the context. CSS typically uses HEX (#FF5733) or HSL (hsl(11, 100%, 60%)), design tools like Figma show RGB and HSL values, print work requires CMYK percentages, and SVG can use any format. The Color Converter accepts a color in any format - type a HEX code, enter RGB values, adjust HSL sliders, or click the color picker to select a color visually - and instantly shows the equivalent in all other formats: HEX, RGB, RGBA, HSL, HSV/HSB, and CMYK. A live color preview swatch updates in real time. Copy any format with one click for direct use in CSS, design tools, or print specifications.

Frequently Asked Questions

How accurate are the unit conversions?

All unit conversions use the exact SI-defined conversion factors published by the International Bureau of Weights and Measures (BIPM). For example, 1 inch is defined as exactly 2.54 centimetres, 1 pound is exactly 0.45359237 kilograms, and 1 litre is exactly 1 cubic decimetre. Temperature conversions use the correct offset formulas (°F = °C × 9/5 + 32) rather than simple multiplication, ensuring accuracy at all temperature values. Results are computed to JavaScript's floating-point precision (approximately 15-17 significant decimal digits) - far more precision than any physical measurement requires.

How do I convert Celsius to Fahrenheit?

The formula is: °F = (°C × 9/5) + 32, or equivalently °F = (°C × 1.8) + 32. For example: 25°C = (25 × 1.8) + 32 = 45 + 32 = 77°F. To convert the other way: °C = (°F - 32) × 5/9. For example: 77°F = (77 - 32) × 5/9 = 45 × 0.556 = 25°C. Common reference points to memorise: 0°C = 32°F (freezing water), 37°C = 98.6°F (body temperature), 100°C = 212°F (boiling water), 20°C = 68°F (comfortable room temperature). The Unit Converter handles this automatically - just select Temperature, enter your value, and choose the units.

What is a Unix timestamp and where do I encounter them?

A Unix timestamp is the number of seconds elapsed since January 1, 1970 00:00:00 UTC (the Unix epoch). You encounter them in: API responses (especially REST APIs returning created_at, updated_at, or expires_at fields), JWT token claims (the exp, iat, and nbf fields are Unix timestamps), database records (many databases store timestamps as integers for efficiency), log files (server logs, application logs, event logs), and JavaScript (Date.now() returns milliseconds since epoch - a 13-digit number). The current timestamp is approximately 1.7 billion seconds (1,700,000,000+). If you see a 10-digit integer in data that represents a date, it is almost certainly a Unix timestamp in seconds.

What color format should I use in CSS?

For modern CSS: use HSL for colours you want to programmatically adjust (creating shades, tints, and hover states by changing just the Lightness value is very intuitive in HSL). Use HEX for fixed colours that you do not need to adjust - it is the most compact notation and universally understood. Use RGB or RGBA when you need an alpha/opacity value in older browsers or when your codebase uses RGB throughout. All three formats are supported in all modern browsers. For design systems and CSS custom properties (variables), HSL is increasingly preferred because colour relationships are easier to manage: darken by reducing L, lighten by increasing L, desaturate by reducing S.

How does the Age Calculator handle leap years and different month lengths?

The Age Calculator uses calendar-aware date arithmetic rather than simple day division, which means it correctly handles all the irregularities of the Gregorian calendar. Leap years (where February has 29 days) are accounted for in the day-count calculation. Different month lengths (28, 29, 30, or 31 days) are handled by working with calendar months rather than fixed 30-day approximations. If your birthday is February 29 in a leap year, the calculator shows your birthday as February 28 or March 1 in non-leap years depending on convention. The age in years is always calculated from calendar anniversary to calendar anniversary, matching how age is legally defined in most jurisdictions.