There are three main pages for three types of calculations: Exposure, Photometric, and Contrast. Navigation between pages is possible by swiping left or right, or by tapping the buttons on the navigation bar.

Tapping twice anywhere on the page opens the main menu with access to Settings, Aperture Table, ISO Table, Shutter Speed Table, and About pages. These pages can be closed by swiping down.

To open the Settings page, open the Menu page by tapping twice anywhere on any of the three calculation pages (Exposure, Photometric, or Contrast), and then select Settings. 

Exposure time can be expressed as a combination of frames per second and shutter opening (video style), or as fractions of a second (photo style).

A light meter constant (C) is used in some of the calculations. Because it is a lesser-known property of light meters, Wikipedia provides a brief explanation: "the constant C should be chosen by statistical analysis of the results of a large number of tests carried out to determine the acceptability to a large number of observers of a large number of photographs for which the exposure was known, obtained under various conditions of subject matter and over a range of luminances." LuxCalc user should choose the value for his or her light meter or the generic (default) value of 330.

Exposure time, aperture opening and sensitivity can be calculated to the precision of a full stop, half stop, one third of a stop or all three at once (default).

Luminance and distance values are expressed in metric units (lux and meter) by default. If the "Imperial measures" switch is selected, these values are expressed in imperial units (foot candles and feet).

Calculated aperture and ISO values are rounded to standard values by default. If the "Show raw values" switch is selected, raw calculated values will be displayed below rounded values.

If the "Sync luminances" switch is checked, luminance related values calculated on one page will automatically be synced to corresponding parameters on other pages. For example, the luminance value calculated on the Exposure page will be synced to the luminance parameter on the Photometric and the key light parameter on the Contrast page. The key light value calculated on the Contrast page, if expressed as an aperture number, will be synced to the aperture parameter on the Exposure page. The condition for syncing is that the destination parameter is not selected as the calculation target.

The "+/-aperture notation" switch selects how aperture values are expressed. By default, they are expressed as standard f-stop numbers (e.g. 6.3), but descriptive values (e.g. 5.6+) can be used as an alternative.

To make a calculation, select the parameter you wish to calculate by tapping on it. Selected parameters are colored and are always on top. Next, enter the values for all the input parameters. Use sliders to set values for aperture, sensitivity, and shutter speed. When all input parameters are defined, the value of the output parameter is calculated. 

If you change the value of an input parameter, the value of the output parameter is calculated accordingly. If you select another parameter, it moves to the top and its value is calculated using the current input parameters.

You can clear the values of all the parameters by tapping on the button Clear.

Calculates interrelations between luminance (in lux or foot candles), aperture opening, sensitivity, and exposure time. Aperture openings can be expressed as numeric (e.g. 6.3) or descriptive (e.g. 5.6+). A preferred style can be chosen on the Settings page. 

For parameters which are commonly presented as rounded to certain predefined values (aperture, ISO, and shutter speed), there is the option to show their raw calculated value along with the rounded value. This option can be enabled or disabled on the Settings page. 

There are two ways to express exposure time: video style as a frame per second / shutter opening or in seconds. It can be selected on the Settings Page.

Calulation uses the formula:

(aperture squared) / exposure time (sec) = (luminance (lux) * ISO) / constant C

Calculates interrelations between luminance (in lux or foot candle), light intensity (in candela) and distance (in meters of feet), using the formula: intensity (candela) = luminance (lux) / (distance (m) squared)

The key light to fill light ratio is calculated using the formula: (key + fill) / fill.

The contrast is usually calculated from key light and fill light luminance values expressed in lux or foot candle. LuxCalc, however, has the option to calculate contrast from key light and fill light aperture readings. Cinematographers and videographers used to thinking in f-stops may find this option convenient.

Aperture, ISO and shutter speed values are usually presented not in their calculated, but in commonly accepted rounded values. For example, aperture opening calculated as 5.657 would be presented as 5.6 in literature, on lens and light-meter scales etc. 

Aperture, ISO and Shutter Speed Tables show the range of rounded values used by LuxCalc for calculations. Each table has four rows: first row represents full stops, while second, third and fourth row present one third, half and two thirds increments. Aperture range is between f 1 and f 22, ISO range is between 6 and 25600, and shutter speed is between 30 seconds and 1/4000 second.

Aperture table can be very helpful when interpreting digital light meter readings, because it is not easy to remember that the difference between f 3.2 and f 3.6 is 1/3 of a stop. Aperture table has option to show raw instead of rounded values. Raw values are used in all calculations.