RoChess! Tool · Updated 2026-10-28
RoChess! Elo calculator
This adds K times the gap between your result and the expected score. It is textbook Elo, not a readout from the RoChess! server.
The two lines the form uses
Expected score is 1 / (1 + 10 ^ ((opponent − you) / 400)). The new rating is your rating plus K times (result − expected). A win is 1, a draw is 0.5, a loss is 0.
Worked example at K=32, you 1200, opponent 1400: expected score about 0.240. A win is about +24.3 (new 1224). A draw is about +8.3. A loss is about −7.7. Same rating versus same rating, a win is +16.
Read why this may not be the live system before you treat the output as your next RoChess number. The Spanish page embeds the same warning.
Which K to pick
FIDE’s published bands, from the handbook notes we logged, are K=40 for a new player through 30 games, K=20 below 2400, and K=10 after a player has reached 2400. Many chess sites use K=32. None of those bands is a RoChess! rule. If you do not know a K, leave 32 and treat the result as a scale, not a prediction.
Player pools and bot scores are discussed on bots and stats.
Estimate a rating change
Formula from the Elo rating system article on Wikipedia. This is not a RoChess! server formula.
Questions
Is this the official RoChess! calculator?
No. The game has not published a formula. This page only runs classic Elo so you can compare.
What K does RoChess! use?
Unknown. The selector is there so you can try 10, 20, 32, or 40.
Why is a win against a higher rating worth more?
Because the expected score was lower, so the gap between 1 and that expectation is larger.
Can I enter a RoChess bot rating?
Only if you already have a number from your own game screen. This site does not have an official 19-bot rating table to preload.
Keep reading
Sources and last checked (UTC)
- Wikipedia: Elo rating system — Expected score and update rule.
- FIDE handbook B.02 — K bands. Not a RoChess rule.
- Roblox games API — Confirms the formula is absent. 2026-10-28.