extern string     MM_Parameters    = " MoneyManagement by L.Williams ";
extern bool       MM               =   true; // ÌÌ Switch
extern double     MaxRisk          =    0.04; // Risk Factor
extern double     LossMax          =       0; // Maximum Loss by 1 Lot

<------------------------------------------------------

double MoneyManagement()
{
   double lot_min =MarketInfo(Symbol(),MODE_MINLOT);
   double lot_max =MarketInfo(Symbol(),MODE_MAXLOT);
   double lot_step=MarketInfo(Symbol(),MODE_LOTSTEP);
   double contract=MarketInfo(Symbol(),MODE_LOTSIZE);
   double vol;
//--- check data
   if(lot_min<0 || lot_max<=0.0 || lot_step<=0.0) 
   {
   Print("CalculateVolume: invalid MarketInfo() results [",lot_min,",",lot_max,",",lot_step,"]");
   return(0);
   }
   if(AccountLeverage()<=0)
   {
   Print("CalculateVolume: invalid AccountLeverage() [",AccountLeverage(),"]");
   return(0);
   }
//--- basic formula
   if ( MM )
   {
   vol=NormalizeDouble(AccountFreeMargin()*MaxRisk*AccountLeverage()/contract,2);
   Print("Margin=",AccountFreeMargin()," r=",MaxRisk," lev=",AccountLeverage()," cont=",contract);
   }
   else
   vol=Lots;
//--- check min, max and step
   vol=NormalizeDouble(vol/lot_step,0)*lot_step;
   if(vol<lot_min) vol=lot_min;
   if(vol>lot_max) vol=lot_max;
//---
   return(vol);
}   

<------------------------------------------

then use it like example below

OrderSend(Symbol(),OP_SELL,MoneyManagement(),Bid,3,SL,TP,KOMEN,MAGICNO,0,Red);