neilt org

elevation [0-9999]ft, qnh [800-1100]hpa: uses rot 27 ft per mb to calculate pressure altitude. formula elevation + ((std - qnh) * 27)). of course elevation + ((std - qnh) * 30) is easier to calculate without tools and might still be good enough for government work:-) we calculate pressure altitude to use in our density altitude calculation.
temperature and dewpoint [-40-60] degrees centigrade. density altitude is commonly calculated without taking humidity into account. check the box to calculate density altitude using a very rough 20 * dew point addition to the dry air calculation. i suggest rounding up to the next whole 1000 ft; conservative. the full calculation for density altitude including humidity is beyond my ken:-)