On the other hand, the relative humidity changes radically during the day as the air temperature changes. My old relative horsepower calculator using relative humidity is still available. Also, take a look at my Density Altitude calculator. To use this calculator, just enter the air temperature, barometric pressure, dew point and altitude. Then click on the calculate button.
Air density is affected by the atmospheric pressure, temperature and humidity.
On a hot day, or at high altitude, or on a moist day, the air is less dense. A reduction in air density reduces the amount of oxygen available for combustion and therefore reduces the engine horsepower and torque. This calculator shows you how much the air conditions on any given day will alter the horsepower of a normally aspirated internal combustion engine. The dyno correction factor shown above is the reciprocal of the relative horsepower number. The dyno correction factor, the actual air pressure and the vapor pressure are included for comparisons to DynoJet chassis dyno test data.