Everyday numbers
Interactive tools with transparent methods. Change the inputs, check the example and use the result with its assumptions.
Percentage Calculator
Calculate a percentage of a base value and the value after that percentage is added or removed. Enter a negative base only when it makes sense for your task.
Aspect Ratio Height Calculator
Matching height equals width multiplied by ratio height divided by ratio width. At a 16:9 ratio, a width of 1,920 pixels gives a height of 1,080 pixels.
Screen Pixel Density Calculator
Pixel density equals the diagonal pixel count divided by the diagonal screen size in inches. The diagonal pixel count comes from the square root of width squared plus height squared.
Raw Image Memory Calculator
Raw image bytes equal width × height × channels × bytes per channel. A 1,920 × 1,080 buffer with four one-byte channels occupies 8,294,400 bytes before other memory overhead.
CSS Pixel to Device Pixel Calculator
Multiply each CSS dimension by device pixel ratio to obtain backing dimensions. An 800 × 600 CSS-pixel area at a ratio of 2 needs 1,600 × 1,200 device pixels.
Hours Minutes Seconds Calculator
Total seconds equal hours × 3,600 plus minutes × 60 plus seconds. A duration of 1 hour, 30 minutes and 15 seconds equals 5,415 seconds or 90.25 minutes.
Two-Value Weighted Average Calculator
A weighted average equals the sum of each value multiplied by its weight, divided by total weight. Values of 80 and 100 with weights 3 and 1 have a weighted average of 85.
Percent change vs percentage points in campaign reports
Percentage-point change subtracts two percentages. Relative percent change divides that difference by the original percentage. A rate rising from 2% to 3% gains 1 percentage point and increases by 50%.
Wilson interval table: the uncertainty behind a conversion rate
An observed 10% conversion rate is less precise with 100 eligible trials than with 10,000. Wilson intervals show sampling uncertainty under a binomial model; they do not prove that an ad variant is better or that future traffic will behave the same way.
Aspect-ratio dimensions for images and design canvases
Aspect ratio is width divided by height. To preserve a ratio w:h, height equals width × h ÷ w. A 16:9 canvas at 1,280 pixels wide is 720 pixels high.
Percentage decrease and the increase needed to recover
After a percentage decrease, the same percentage increase does not restore the original base. A 20% decrease requires a 25% increase on the smaller value.