HELIUM has a lift of .84 ounces per cubic foot at sea level.
To determine the volume of a balloon in cubic feet, multiply the cube of the radius in inches by 1.333, multiply the result by 3.1416, and then divide by 1728. diameter/2= Radius, radius *12 for radius in inches=ri, ri*ri*ri*3.1416/1728=cubic foot
To determine the lift of a helium filled balloon, multiply the volume in cubic feet by .84 to determine ounces, Divide ounces by 16 to determine pounds.
Lift is reduced approximately 7.5% for each 1000 feet above sea-level.
The information contained in this chart is computed at sea-level and is approximate.
Volume may vary due to over-inflation or under-inflation of the balloon.
Lift, and flying time are effected by such things as helium quality, weather, humidity, temperature, atmospheric conditions, and elevation above sea-level. As a "rule of thumb", reduce lift and flying time by 7.5% for each 1000 feet above sea-level.