You don't have control over iDevice size output. Panoweaver and Tourweaver look after the output sizes of 500px (cube faces) for iPhone and 955px (cube face) for iPad.
Based on these sizes and multiplied by Pi the 2:1 equirectangular sizes are 1570px and 3000px respectfully.
Pixel size is not your only concern, you also must consider the weight size of each panorama as mobile devices are normally on the low size for memory and processing power.
A simple rule of thumb is 2.5x the size of the screen resolution if possible.