Date Difference Calculator

Percentage Calculator shows three independent calculators at once, each with its own pair of inputs. "What is X% of Y" multiplies, so 20% of 50 is 10; its result is printed unrounded, so 33% of 10 reads as 3.3000000000000003. "X is what % of Y" divides X by Y and multiplies by 100, rounded to two decimals; if Y is 0 it returns 0 rather than an error. "% change from X to Y" is (Y minus X) divided by the absolute value of X, times 100, rounded to two decimals; if the starting value X is 0 and Y is not, the field shows "Infinity%". Negative values work, and an empty field counts as 0. Everything is computed in the page as you type.

Calculate a simplified aspect ratio from a width and height in your browser — enter dimensions like 1920 by 1080 and get the simplified ratio (16:9), computed using the greatest common divisor rather than a rounded approximation. You can also calculate a proportional new width or height: enter an original width and height, then a new width to get the matching height (or a new height to get the matching width), keeping the same proportions. It is handy when resizing an image or video frame by hand, checking what aspect ratio a resolution corresponds to, or working out a proportional crop size before using it in an editor. Everything is calculated locally in your browser, so no dimension you enter is ever sent to a server or stored anywhere.

Unix Timestamp Converter turns a Unix timestamp into a readable date and turns a date back into a Unix timestamp, entirely in your browser. Paste a timestamp and choose Seconds, Milliseconds, or Auto — Auto reads a value below 100,000,000,000 in size as seconds and anything larger as milliseconds, and you can always force the unit. It shows the instant as UTC (for example 2026-08-29 19:30:00 UTC), as your local time labelled with the browser time zone name such as Europe/Paris, and as an ISO 8601 / RFC 3339 string like 2026-08-29T19:30:00.000Z, plus the value normalised to both Unix seconds and Unix milliseconds. Going the other way, enter a date and time, pick UTC or your local zone, and read the Unix seconds, milliseconds, and ISO output. Timestamp 0 is 1970-01-01T00:00:00Z and negative timestamps point before 1970. Local conversions use the browser's own daylight-saving rules: a wall-clock time skipped at the spring change is shifted and flagged, and a time repeated at the autumn change resolves to one instant. Precision is one millisecond; nanoseconds are not supported, and values outside the range JavaScript dates can represent are rejected. This is a format converter, not a duration calculator: to measure the gap between two dates, use the Date Difference Calculator. Nothing you enter is uploaded.

Length Converter turns one value into another length unit across metres, kilometres, centimetres, millimetres, miles, yards, feet and inches. It converts through metres using exact factors — a mile is 1609.344 m, a yard 0.9144 m, a foot 0.3048 m and an inch 0.0254 m, the international definitions — so metric and imperial results line up to the precision shown. The answer is displayed to four decimal places, which is a display rounding rather than the stored value. Only these eight units are offered: there is no nautical mile, micrometre, nanometre, thou or mil. Pick the from and to units and the result recalculates whenever you change the number or a unit. The calculation runs in the page and nothing is sent anywhere.