Start with the full item table
A Rust case normally has a price, a list of possible items and a probability for each outcome. The first check is whether every item and probability is available before opening. Promotional tiles often emphasize rare expensive skins, but the common low-value outcomes determine most of the expected return.
The probabilities should total 100%, subject only to a clearly explained rounding difference. If an item list is visible but probabilities are absent, the page does not contain enough information to calculate expected value.
Expected value in plain language
Multiply each item’s credited value by its probability and add the products. The result is the average credited value predicted over a very large number of identical openings. It is not the amount a person should expect from a single case.
Suppose a five-unit example case has a 70% chance of a one-unit item, a 25% chance of a four-unit item and a 5% chance of a twenty-unit item. Its expected credited value is 0.70×1 + 0.25×4 + 0.05×20 = 2.70 units. Dividing 2.70 by the five-unit price gives an implied return of 54%. These numbers are examples, not live operator data.
Credited value is another assumption
The calculation uses the values displayed by the site. Those values may differ from Steam Community Market observations, third-party cash markets or the price attached to current withdrawal stock. A transparent case table can therefore describe its internal mathematics without guaranteeing an external resale value.
Read how Rust skins are valued before treating site balance and market value as interchangeable.
Roll mapping and provably fair checks
Some systems convert a cryptographic output into a number across a fixed range, then map ranges to items. A completed-round check should let a reader verify the committed server seed, client seed, nonce and calculation used for the roll. The item table must still show which roll range corresponds to which item.
The verifier answers “did this recorded input produce this recorded roll?” It does not answer “was the case priced attractively?” The provably fair guide separates those questions.
Case opening versus case battles
A battle may use the same underlying case outcomes but adds a winner rule across multiple players or teams. Check whether the highest total, lowest total or another mode wins, and whether a separate fee applies. Our case battle modes guide covers those structures.
The case-opening site comparison lists operators whose public catalogues name case opening. Inclusion does not mean every case publishes enough data for a complete calculation.