What are you trading? Pyramiding fits only strong trends trading, and means that subsequent buys should be successively smaller (like a pyramid). The size of your trade is determined by your account size, your expectancy, and your drawdown toleration. Once you have a consistently positive expectancy you can optimize your position size. Until then keep your size small. Most people recommend risking up to 1-2% per position, 5-6% per account. When you trade long your risk is defined as: number_of_shares * (cost_basis - stop_loss).