JSFiddle - React, Tailwind, and code Playground

JavaScript

function Balloon() {
    function density(altitude, theGas) { /* KG/CU M */
        
        var gas = { /* GAS DEFINATIONS - wolframalpha.com */
            "hydrogen": .00100794,
            "helium": .004002602,
            "nitrogen": .0140067,
            "methane": .0160425,
            "ammonia": .0170305,
            "neon": .0201791,
            "dry air": .0289644
        }

        var alt = { /* CONSTANTS - http://en.wikipedia.org/wiki/Density_of_air#Altitude */
            "p0": 101325,
            // Sea level standard atmospheric pressure (Pa)
            "T0": 288.15,
            // Sea level standard temperature (K) 
            "g": 9.80665,
            // Earth-surface gravitational acceleration (m/s^2)
            "L": 0.0065,
            // Temperature lapse rate (K/m)
            "R": 8.31447 // Universal gas constant (mol * K)
        }

        var temperature = alt["T0"] - alt["L"] * altitude;
        var pressure = alt["p0"] * (1 - ((alt["L"] * altitude) / alt["T0"])) ^ ((alt["g"] * gas[theGas]) / (alt["R"] * alt["L"]));
        var density = (pressure * gas[theGas]) / (alt["R"] * temperature);

        return density;
    }

    function lift(altitude, gas) { /* KG/CU M */

        return density(altitude, "dry air") - density(altitude, gas);
    }

    this.requiredGas = function(altitude, gas, ratio, weight) {
        return ((weight / 1000) * ratio) / lift(altitude, gas);
    }
}

balloon = new Balloon();
var required = balloon.requiredGas(10, "helium", 1.5, 4530);
alert(required);