Steam Siege Mega EX Pull Rate — 5.56% per pack (1 in 18)
5.56% of Steam Siege booster packs contain a Mega EX card — roughly 1 in 18 packs. Steam Siege ships 2 Mega EX cards in the pool, so the chance of pulling any specific Mega EX is 0.0278 (≈1 in 36). These percentages come from PackRip's own rate table (the same constants the simulator runs on) — they are a model of the product, not a measurement of it. The Pokemon Company has never published pull rates.
Steam Siege Mega EX pull-rate methodology
| Formula | Tier odds = 5.56% per pack; per-card odds = tier odds ÷ 2 Mega EX cards = 1 in 36. |
|---|---|
| Assumptions | One independent rare-slot roll per pack; uniform selection within the tier; no pity timers, box mapping, short-print correction, or edition/condition split. |
| Data source | Set checklist and rarity labels from the bundled Pokemon TCG API catalog; tier rates from rareSlotRates(), mirrored from the live pack opener. |
| Update cadence | Regenerated by prerender whenever set metadata, catalog data, or pull-rate constants change. |
| Limitations | This is a theoretical per-pack rate. Real sealed product can show print-run variance, collation quirks, and market-specific edition differences. |
Mega EX cards in Steam Siege
| # | Card | TCGplayer market | Per-card odds |
|---|---|---|---|
| 1 | M Gardevoir-EX #79 | $22.07 | 1 in 36 |
| 2 | M Steelix-EX #68 | $11.24 | 1 in 36 |
How the 5.56% rate is computed
Every Steam Siege booster pack rolls one rare-slot card (plus uncommons, commons, and energy in fixed slots). The rare slot is itself a weighted random draw across 7 tiers — Rare, Holo Rare, Mega EX, and the era's other chase rarities. The Mega EX tier captures 5.56% of those rare-slot draws (= 5.56 packs out of every 100). Within the Mega EX tier, all 2 cards share the slot uniformly, so per-card odds are 5.56% ÷ 2 = 0.0278 = 1 in 36.
This is the same math PackRip's live Steam Siege simulator uses to roll packs — open as many as you want for free, watch the empirical hit rate converge to the theoretical 5.56% over a large enough sample. Source code lives in src/utils/packGenerator.ts and the per-rarity drift is build-time-asserted against the published rates so the simulator and this landing page can never disagree.
Cumulative probability — how many packs to hit Mega EX
Mega EX pulls follow a geometric distribution with per-pack rate 0.055600. The expected number of packs until your first Mega EX hit is 18; at 95% confidence you'll have one within 53 packs. Most experienced openers crack a sealed booster box (36 packs) and hit Mega EX with probability 87.2% — so the average box yields just over 2.0 Mega EX pulls.
Related on PackRip
- Open Steam Siege packs free — same pull rates, live RNG
- Steam Siege binder completion calculator
- Steam Siege per-pack expected value
- Top 25 most valuable Steam Siege cards