Definition
Unit is a standardized bet size used to track performance without exposing actual dollar amounts. Typically defined as 1% of starting bankroll. Expressing results in units ("+4.2u", "−1.5u") allows comparison across bettors with different bankroll sizes. Unit size should remain fixed or adjust only with Kelly-based calculations. Varying unit size without a principled system inflates winning streaks and obscures true ROI. Most serious bettors track records exclusively in units.
Worked Example
Starting bankroll: $5,000. Unit size: 1% = $50. Win 3 bets at −110 ($55 each): +$150 profit = +3 units. Lose 2 bets at −110 ($55 each): −$110 = −2.2 units. Net: +0.8 units = +$40. If bankroll grows to $6,000, unit grows to $60 — keeping position sizing proportional to capital.
Why It Matters
Consistent unit sizing enables accurate ROI measurement and prevents emotional position inflation after wins or desperation sizing after losses — both of which destroy long-run results.