var memoryUsedInKb:Number= Number(System.totalMemory/1024).toFixed(2);

private function calculateUsedBytes(unit:String):String
{
    var p:uint = pows[unit.toLowerCase()];
    var t:Number = Number(System.totalMemory/Math.pow(2,p))
    var d:uint = digits[unit.toLowerCase()];
    return t.toFixed(d).toString();
}

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" 
    width="237" creationComplete="init()" height="255">
    <mx:TextInput x="67" y="131" id="stringToRepeat" text="abcdefghijklmnopqrstuvw" 
        toolTip="The string that will be added"/>
    <mx:Label x="9" y="133" text="String:"/>
    <mx:Label x="9" y="159" text="Repeat:"/>
    <mx:NumericStepper x="67" y="157" id="timesToRepeat" stepSize="10" minimum="0" 
        maximum="1000000" width="99" toolTip="How many times the string will be added" 
        value="10000"/>
    <mx:Button x="174" y="157" label="+" width="22" click="handleAlocate(event)" 
        toolTip="Alocate"/>
    <mx:Label x="9" y="203" text="Memory:"/>
    <mx:HRule x="9" y="187" width="217" height="8"/>
    <mx:HRule x="10" y="115" width="217" height="8"/>
    <mx:Label x="67" y="203" width="159" id="kbUsed" text="{memoryUsed}"/>
    <mx:ComboBox x="171" y="201" width="55" id="unitCombo" dataProvider="{units}"
        change="handleUnitChange(event)" toolTip="Units"/>
    <mx:Label x="9" y="229" text="Length:"/>
    <mx:Label text="{arrayLength}" x="67" y="229" width="87" 
        toolTip="The length of the array containing the strings"/>
    <mx:Button x="204" y="157" label="x" width="22" click="handleClear(event)" toolTip="Clear"/>
    <mx:Text x="10" y="10" text='This is an example to show memory usage. Use the string and 
        the repeat stepper to alocate more memory. Pressing "+" button will add the 
        string n times as selected into repeat to an array. The "x" button is for 
        clearing out the array.' width="217" height="102"/>
    <mx:Script>
        <![CDATA[
            [Bindable]
            private var units:Array = [{label:"B",data:"b"},{label:"KB",data:"K"},
                {label:"MB",data:"m"},{label:"TB",data:"t"}];
 
            private var pows:Object = {b:0,k:10,m:20,t:30};
            private var digits:Object = {b:0,k:0,m:2,t:4};
 
            [Bindable]
            private var memoryUsed:String;
 
            [Bindable]
            private var arrayLength:uint;
 
            private var useDump:Array = new Array();
 
            private function init():void
            {
                memoryUsed = calculateUsedBytes("k"); 
                unitCombo.selectedIndex = 1;
                arrayLength = useDump.length;
            }
 
            private function calculateUsedBytes(unit:String):String
            {
                var p:uint = pows[unit.toLowerCase()];
                var t:Number = Number(System.totalMemory/Math.pow(2,p))
                var d:uint = digits[unit.toLowerCase()];
                return t.toFixed(d).toString();
            }
 
            private function handleUnitChange(event:Event):void
            {
                memoryUsed = calculateUsedBytes(unitCombo.selectedItem.data);
            }
 
            private function handleAlocate(event:MouseEvent):void
            {
                var r:uint = timesToRepeat.value;
                var s:String = stringToRepeat.text;
                for (var i:uint = 0; i < r; i++)
                    useDump.push(s);
 
                memoryUsed = calculateUsedBytes(unitCombo.selectedItem.data);
                arrayLength = useDump.length;
            }
 
            private function handleClear(event:MouseEvent):void
            {
                useDump = new Array();
 
                memoryUsed = calculateUsedBytes(unitCombo.selectedItem.data);
                arrayLength = useDump.length;
            }
 
        ]]>
    </mx:Script>
</mx:Application>