function quantityNeeded(spreadrate, SF, unitSize) {
var spreadRate=spreadrate;
var SqFeet=document.spreadCalc.SF.value;
var UnitSize=unitSize;
var unitsNeeded=Math.ceil(SqFeet/spreadRate);
if (SqFeet < 1)
alert("You must inlude a number 1 or greater to make your calulation");

else

alert("We recommend that you order : " + unitsNeeded + " Gallons. (2 coats x " + (spreadRate * 2)  + " Square Feet per Gallon per Coat)");
}