Risk-adjusted return, not just return
A strategy that makes 40% a year with wild swings can be worse than one making 15% smoothly β the Sharpe ratio is how you compare them honestly. Pair it with the expectancy calculator and Kelly criterion to size the edge.
Return per unit of risk β the number fund managers actually care about
Sharpe ratio = (portfolio return β risk-free rate) Γ· standard deviation of returns. A Sharpe of 1.0 means you earn 1% excess return per 1% of volatility. Above 1.5 is considered good. Above 2.0 is exceptional and rare over long periods.
The risk-free rate (US T-bill rate, currently around 4.5%) is subtracted because that's what you'd earn doing nothing. A strategy returning 12% with Sharpe 0.8 is arguably worse than one returning 8% with Sharpe 1.4, because the 12% strategy takes on more volatility per unit of return.
For crypto the risk-free benchmark is debatable β some use 0%, some use T-bill rates, some use BTC buy-and-hold. Your Sharpe looks very different depending on the benchmark. A strategy that returns 80% but with 120% annualized volatility has a Sharpe below 0.7 even before subtracting risk-free rate.
Related: Sortino ratio (downside-only volatility), Calmar ratio (max drawdown), ROI calculator.