MTG Tempest's Land Calculator

v2.0.1

Based on the math by Frank Karsten

All credit to Scryfall for the Tagging Service!

31.42 + 3.13 × average mana value − 0.28 × (cheap card draw / mana ramp spells). Calibrated for a 100-card deck, with MDFCs counted partially as lands. Find the average Mana Value of your SPELLS and move the slider to match. If you would like a generalized analysis of your deck's draw + ramp, then paste and analyze your deck below. If not, you may move the slider manually.
37–38 Approximate minimum
number of lands
31.42 + 3.13 × 3.00 − 0.28 × 12 = 37.45
Start with 42 lands. Cut one land for roughly every 3–4 cheap card draw or mana ramp spells.

Decklist

Paste a decklist in the MTGO format. This only works with a 100-card list and will fail to check any cards with alternative names from "the Omenpaths". Any SIDEBOARD: or MAYBEBOARD: section is ignored. It checks Scryfall's Tagger data for cards tagged ramp or draw with mana value below 4 (which includes lands), then updates the "cheap card draw / mana ramp spells" slider and the average mana value slider above automatically after analysis. This is the only part of the app that needs internet. It calls Scryfall's public API for a moment when you click Analyze.

Hypergeometric Calculator

Exact odds of drawing a given number of "successes" (lands, removal, whatever card type you're tracking) out of the cards you've seen so far. Uses arbitrary-precision integer math, so there's no floating-point rounding error.
e.g. number of lands, ramp spells, or a card category
opening hand + draws by the turn in question
Exactly t
At least t
At most t
Full probability distribution (highlighted bar = target t)
Probability
Number of successes (t)