function load_size()
{
//declare variables
var load;
var voltage;
var length;
var result;
var voltage_select;

//get values
load = document.forms[0].load.value;
length = document.forms[0].length.value;
voltage_select = document.forms[0].voltage.selectedIndex;
voltage = document.forms[0].voltage.options[voltage_select].value;

//calculate result
result = ((load / voltage) * 0.04 * length) / (voltage * 0.05);

//validate
var verify = isNaN(result);
if (verify) {
	alert ("Bütün Girdiler Rakam Olmalıdır");
	return false;
	};

//rounding
if (result < 4)
	//round to nearest half
	{
	result = result * 2;
	result = Math.ceil(result);
	result = result / 2;
	}
else
	{
	if (result < 6) result = Math.ceil(result);
	
	else
		{
		result = result / 5;
		result = Math.ceil(result);
		result = result * 5;
		};
	};

//write total
document.forms[0].result.value = result;
}