A "rating", per se, does not apply to Ponds. Ratings measure the likely outcome of one player against another when the game has completely opposite goals -- in chess, checkmating the opponent.

Ponds is a "free for all" or "every person for themself" game.

So, a meaningful measurement would be how long you can stay in the pond.

An "average ranking" of your Pond performance, weighted by the number of players per pond, provides the most meaningful information.

In this case, the lower the number, the better.

But how can you qualitatively assess your overall performance?

Easy.

For each pond game you are in, multiply your final position by the number of players in that pond. Divide this by the sum of all players in every pond you played in.

For example, suppose you came in first place in 3 different pond games, each with 16 players. And you can in 14th place in a pond with 200 players.

How does this compare with someone who came in 2nd place in a pond of 50, 5th place in a pond of 75, and 11th place in a pond of 200?

It is not immediately apparent, so do this:

Player A

3 first place finishes:
(1 x 16) + (1 x 16) + (1 x 16) = 48

1 finish in 14th place
(14 x 200) = 2800

Sum of all pond players = 16 + 16 + 16 + 200 = 248

So add 2800 to 48, and divide by 248

Player A = 2848/248 = 11.48

Now Player B would have a performance rating of (2 x 50) + (5 x 75) + (11 x 200) = 2675 divided by (200 + 75 + 50), so...

Player B = 2675/325 = 8.23

Player B would actually have a better performance than Player A, overall.