CS2 Collection Completion Calculator
Calculate the expected number of cases you need to open to collect all unique skins from a CS2 case. This tool uses the Coupon Collector's Problem mathematics to provide accurate estimates for completing your collection.
Collection Completion Calculator
Enter the skin counts for each rarity tier to calculate completion estimates
Quick Case Presets
Number of Unique Skins Per Rarity
Calculation Options
Collection Completion Analysis
Expected outcomes for completing your collection
Difficulty by Rarity Tier
| Rarity | Skins | Expected Cases | Contribution |
|---|
Probability of Completion by Case Count
Direct Purchase Comparison
Opening cases to complete a collection is typically far more expensive than buying skins directly. Check the Steam Community Market to compare prices for individual skins in your target case.
Understanding Collection Completion Probability
The Coupon Collector's Problem
The mathematics behind collecting all skins from a CS2 case is known as the Coupon Collector's Problem in probability theory. This classic problem asks: if there are n different types of coupons (skins), and each draw gives you a uniformly random coupon, how many draws do you need to collect all n types?
The expected number of draws follows the formula:
For example, if a tier has 7 unique skins, the expected number of drops at that tier to collect all 7 is:
E[T] = 7 × (1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + 1/7) ≈ 7 × 2.593 ≈ 18.15 drops CS2 Case Complexity
CS2 cases add complexity because different rarity tiers have drastically different drop rates. Collecting all 7 Mil-Spec skins is relatively straightforward since they drop 79.92% of the time, but collecting all 2 Covert skins is extremely difficult since they only drop 0.64% of the time.
According to Valve's official CS2 case odds, the drop rates are:
- Mil-Spec (Blue): 79.92% chance per case
- Restricted (Purple): 15.98% chance per case
- Classified (Pink): 3.20% chance per case
- Covert (Red): 0.64% chance per case
- Rare Special (Gold): 0.26% chance per case (knives/gloves)
Our calculator accounts for these varying drop rates when estimating how many cases you'll need to open to complete your collection goal.
Why Covert Skins Dominate the Cost
Even though there are typically fewer Covert skins in a case (usually 2), they represent the majority of the difficulty in completing a collection. This is because:
- Low Drop Rate: At 0.64%, you'll average ~156 cases per Covert drop
- Duplicate Problem: Once you have 1 of 2 Covert skins, you have a 50% chance of duplicate
- Compounding Effect: The last Covert skin requires ~312 more cases on average
Research from Nature Human Behaviour has shown that players often underestimate how long it takes to collect complete sets from randomized systems, making tools like this calculator valuable for setting realistic expectations.
StatTrak Considerations
If you want to collect StatTrak variants of all skins, the difficulty increases dramatically. StatTrak items only have a 10% chance of appearing on any drop, meaning you need approximately 10x more drops at each tier to get the StatTrak version of a specific skin.
For more details on StatTrak mechanics, see our Complete StatTrak Guide.
Related Tools
Frequently Asked Questions
Is it cheaper to buy skins directly or open cases to collect them?
Almost always, buying skins directly from the Steam Community Market is significantly cheaper than opening cases to collect them. Our calculator shows the expected case opening cost, which is typically 3-10x higher than buying the skins directly. The exception might be extremely rare cases with valuable floor prices, but even then, direct purchase is usually more economical.
How accurate is the expected cases number?
The expected cases number is mathematically accurate based on probability theory. However, it represents the average across infinite attempts. In practice, you might need significantly more or fewer cases due to random variance. About 37% of players will need more than the expected number, and some may need 2-3x as many due to bad luck.
Why does collecting Covert skins require so many cases?
Covert skins have a 0.64% drop rate, meaning on average you'll open 156 cases per Covert drop. Combined with the coupon collector effect (needing all unique skins, not just any Covert), the last Covert skin becomes extremely expensive to obtain through case opening. This is why direct purchase is almost always more economical for rare skins.
What about knife and glove collections?
Collecting all knives or gloves from a case is effectively impossible through case opening alone. With 0.26% drop rates and dozens of possible knife/glove types and finishes, the expected cases would number in the hundreds of thousands. If knife collection is your goal, purchasing directly is the only realistic approach.
How does this calculator handle the weighted probability problem?
Our calculator uses a modified coupon collector formula that accounts for CS2's tiered drop system. We calculate the expected cases needed for each rarity tier independently, then take the maximum since you can't complete your collection until you've completed the hardest tier (usually Covert). The math accounts for getting drops at other tiers while waiting for the rare ones.
Should I use this calculator to plan case opening?
This calculator is educational—it shows the true mathematical cost of collection completion. We recommend using it to understand why direct purchase is typically better value, not to plan extensive case opening. If you enjoy case opening for entertainment, set a strict budget unrelated to collection goals. Never open cases expecting to profit or efficiently collect skins.
Last updated: January 2026