Do you need to find a wind chill value? A mixing ratio? A theta-E? No problem. Digital Atmosphere's meteorological calculator lets you plug in values and find a result.
Simply choose the conversion you want at the top, enter the values in the center panel, then press Calculate.
Note about actual pressure. A very important note — when you are asked for "Actual Pressure", this indicates the actual pressure of the parcel, not the sea-level pressure, unless you're really at sea level! You can find your "actual pressure" by simply calculating "Station Pressure (mb)" and entering your altimeter setting (pressure in inches as provided in public weather reports) and your elevation in feet. An example: In Denver, Colorado, your elevation is 5300 ft and the pressure is 29.96 inches. This yields a "station pressure" or "actual pressure" of 834.8 mb. You can then use this value in calculations which ask for "actual pressure".