Roulette Odds & House Edge – The Core Math

European vs American wheels – why the layout matters

Roulette is built around a simple idea: a ball lands in one pocket out of many. The wheel layout determines the probabilities for every bet.

Whenever you compare systems or tools, always specify wheel type. A strategy that looks “almost sustainable” on a European wheel can crumble much sooner on an American one.

You can see these differences clearly in the Roulette Probability Calculator by toggling between European and American wheels.

Odds, payouts and how casinos create an edge

Every roulette bet has:

• True odds
  Based on how many pockets win versus how many exist in total.
• Payout odds
  The ratio the casino pays when your bet wins (for example, 35:1 on a single number).

The house edge comes from the gap between true odds and payout odds.

Example: single-number bet on European wheel

• True chance
  1 winning pocket out of 37 total → 1/37 ≈ 2.70% chance to hit.
• True fair payout
  36:1 would be “fair” if there were no edge (36 losing outcomes, 1 winning).
• Actual payout
  35:1 in standard roulette.

That one unit gap between 36:1 and 35:1 is where the long-term house profit lives.

House edge by common bet type (European wheel)

On a standard European wheel without special rules, most inside and outside bets share the same house edge – about 2.70%. What changes is volatility and hit frequency, not the long-run slice the casino takes.

For definitions of each bet type, see Roulette bet types explained and the roulette glossary.

Expected value (EV) – the house edge in money terms

Expected value (EV) translates odds and payouts into an average gain or loss per unit wagered. It’s basically “house edge in cash”.

Simple EV example

Suppose you bet $10 on red on a European wheel:

• Win chance
  18/37, you gain $10.
• Lose chance
  19/37, you lose $10.

EV per spin = (18/37 × +$10) + (19/37 × −$10) ≈ −$0.27 per spin.

That −$0.27 is the 2.7% house edge applied to your $10 bet. Over 100 identical spins, the long-run average loss is about 100 × $0.27 = $27, even though actual results will vary in the short term.

You can experiment with different bet sizes and spin counts in the EV Calculator.

What house edge means for roulette systems

Now connect this to systems. A system is just a rule for changing your bet size (and sometimes your bet selection) over time – for example, doubling after losses in Martingale or moving along a sequence in Fibonacci.

The key point: no pattern of bet sizing changes the underlying odds or house edge. You’re still playing a game where each dollar wagered has negative expected value.

• Systems can
  Change volatility, how often you win or lose, how deep losing streaks feel, and the emotional experience of a session.
• Systems cannot
  Turn −2.7% into +2.7% on a European wheel, or remove the extra cost of an American wheel.

For a deeper breakdown of system beliefs that conflict with this math, see 7 roulette system myths.

Using tools to see the numbers for yourself

The fastest way to internalize roulette odds and house edge is to plug actual numbers into calculators:

• Probability Calculator
  Check win/lose chances for each bet and wheel type, plus chances of hitting at least once in a session.
• EV Calculator
  Convert those probabilities into expected profit or loss per spin and per session.
• Losing Streak Calculator
  See how often the kind of streaks that break systems are likely to show up.

Once you’ve played with these tools, system claims like “you can’t lose if you just keep doubling” become much easier to evaluate calmly.