To set the total, click on the number after 'Out of' to change it, then press 'set' once you are happy with it.
To calculate a percentage just type the number followed by enter if it does not automatically calculate.
If you are inputting decimal numbers (such as to award half-marks), make sure you enable decimal mode by pressing the 'd' key. This will disable the automatic calculation feature, which is problematic if you are inputting decimals (see 'Why Percentifier is the best').
The answer will be displayed in the left-hand box on the second row (labelled 'last percentage').
A history of your calculations will be displayed in the greeny-yellow section as you calculate.
Notes
Percentages are rounded to the nearest whole number.
History and the total will reset if the page is refreshed.
Why Percentifier is the best (and surprisingly quick):
This tool is optimised for use by teachers calculating percentages on test papers. This is why the total remains the same between calculations.
The answer will automatically calculate itself if the input is the same length as the total unless decimal mode is enabled (as decimal numbers can be longer than the total),
Click 'Show/Hide Help' button above to hide. Happy Percentifying!