Your land count is probably too high, convince me otherwise.

I've seen lots of posts saying that the land count of decks is too low, and while I think that can often be the case, I think it's also wrong most of the time.

I see people advocating for 35+ in all cases, or 40 lands plus ramp, which to me is pretty much always too high (unless you are playing Maelstrom Wanderer or something).

I've been playing commander for 2 decades, and most of my decks have somewhere between 30 and 35 land cards. My rule of thumb from early on was to start at 40, then take 1 out for every 2 ramp cards, take out a full land for a sol ring/mana crypt, and then work from there. I usually count MDFCs/channel lands as half to 1 land, depending on which side the deck usually wants to play, and the ravnica bounce lands count as half a land. This usually ends up in the low 30s. sometimes, for low CMC decks that intend to draw cards a lot (Toski, elfball decks), it can be less than 30.

If the CMC average is high, maybe bump it up a bit, but in that case I'm more likely to leave it a bit lower and just put more ramp cards and efficient draw spells to draw into more lands.

The average changes, but not as quickly as you might think when you swap a few slots. If you use a Hypergeometric calculator, you'll find that the average doesn't change much by changing the number of lands by 5 or so. Ideally, you will get a better result by having a lower land count, mulling aggressively for lands, then drawing more spells. And then use the spare slots for more ramp and especially more card draw.

Most people using a hypergeometric calculator also generally don't count mulligans, and since your opening hand is such a large portion of the cards you will see by turn 4 or so, aggressive mulligans can compensate MASSIVELY for a lower land count, allowing you to get to 4 lands reliably, even if you occasionally have to lose a card or two to mulligans. The London Mulligan helps a lot here, as mulls to 5 can still keep 3-4 land hands, even with lower land counts and can expect to more reliably draw into spells in the mid game. At the end of the discussion, I have a section devoted to using Hypergeometric calcs to calculate if you will reliably get a keepable opening hand.

DISCUSSION:

Most decks with 35-40 land would actually perform better if they simply swapped 3-5 land cards for more draw spells or card/mana advantage ramp spells (ramp that ramps for 2 or more or generates CA as well as ramping). These extra draw spells will compensate for the cards lost in aggressive mulligans, and allow those decks in the mid game to see more cards, and will end up hitting their land drops more reliably anyway. In the late game they shine, since your deck will now have more non-land cards AND more draw spells to draw more of those non-land cards.

People often say that paying for ramp when you don't have a land card in hand is really bad, but I would disagree. Some ramp spells, like Cultivate/Kodama's are essentially built for the low land count decks, since they are best played when you don't have another land drop available. Ramp spells that ramp for 2 or more mana are BETTER than a land if you really need to get more mana under you in the mid game. Even your bog-standard rampant growth isn't bad when you have to play it on a turn where you don't have a land drop; in this 'fail case' you are still hitting your land drop, you just had to pay for it (in other games you will have the land drop AND Rampant growth, allowing you to ramp properly, so you have a 'meh' case, and a good case).

My rationale comes down to deckbuilding and the three possible scenarios that you'll find yourself in regarding land drops. In any given game, you will either:

• Draw a lower-than-average number of lands.
• Draw an average number of lands.
• Draw an above average number of lands.

In a lower land count deck the result of these three scenarios will be:

• Lower-than-average: you'll have to aggressively mulligan, maybe losing a card or two of your starting hand, and maybe will have to play ramp or aggressively play card draw spells to get your lands under you, but you'll still get there, albeit with less board development. If someone pressures you early, you may lose before you get your feet off the ground, but this is multiplayer, so they'll often ignore you in favour of someone who is having a better game, allowing you to catch up. Your higher number of draw spell slots will allow you to pull out of the deficit by the late game, and play comfortably.
• Average: You'll get your early land drops just fine, ramp up to a reasonable amount, then start missing land drops. late in the game you'll draw ramp spells instead of lands, and sometimes have to 'pay for your lands', but by then, you likely have the spare mana that it's not that big of a deal, or you can forgo it because you have enough mana to function anyway.
• Higher-than-average: You'll still be fine most of the time, hitting your land drops every turn, and maybe having a couple left over. Late game, your higher number of spells and ability to have more slots for draw spells will let you draw into more spells and put your foot on the gas, accelerating your plays to be able to get more value than other players.

As you can see, none of these is a fail case. Even in the worst-case scenario, you lose some card advantage in the early game from mulls, will struggle in the mid game, spending ramp just to hit land drops, but will be able to pull out of it in the late game.

On the other hand, with the high land count, 40 land deck; two of the scenarios are good (average and below-average lands drawn), but one of the scenarios is completely unplayable: when you flood out, you will have a bunch of unused land left un-tapped every turn. You'll be more likely to time walk yourself topdecking a land and have less slots for draw spells that could pull you out of it, and when you do draw a draw spell, it's more likely to draw more useless lands. You could use more of your other slots for more draw, but in that case, you will draw EVEN MORE lands, to the point where you can't play them all, and this makes your draw spells worse, since some of the cards they draw are useless.

Essentially: the late game has more fail cases with a higher land count, since flooding out is actually worse than being mana screwed in a multiplayer game. Less land count has less fail cases, since the worst-case scenario just means you have to mull more, and spend a bit of time catching up, but your deck is actually designed to perform better in the late game, so you are more likely to catch up.

For the Math Nerds:

In my opinion Hypergeometric calculations are best used for calculating your chances of getting a keepable opening hand. The following table shows hypergeometric calculations through various numbers of mulligans, with the following assumptions:

• The first or second hands (keeps of 7) will be mulled if they have less than 3 lands, or if they have 5 or more lands.
• A third hand (keep of 6) will be mulled if it has less than 2 or if it has 6 or more lands
• A fourth or subsequent hand won't be kept unless it has at least 2 lands.

Population size:	30	32	34	36	38	40
Chance of needing to mull for <3 lands	64.2%	59.5%	54.7%	50.0%	45.2%	40.6%
Chance of needing to mull for >4 lands	2.5%	3.4%	4.5%	5.8%	7.3%	9.2%
Chance of needing to mull for <2 lands	31.4%	27.4%	23.5%	20.1%	17.1%	14.4%
Chance of needing to mull for >6 lands	0.3%	0.4%	0.6%	0.9%	1.2%	1.6%
Chance to needing to mull the first 7:	66.7%	62.9%	59.2%	55.8%	52.5%	49.8%
Chance to needing to mull a second 7:	44.5%	39.6%	35.0%	31.1%	27.6%	24.8%
Chance to mull a 6 card:	14.1%	11.0%	8.4%	6.5%	5.0%	4.0%
Chance to mull a 5 card:	4.4%	3.0%	2.0%	1.3%	0.9%	0.6%
Chance to mull a 4 card:	1.4%	0.8%	0.5%	0.3%	0.1%	0.1%

Note that the population size in each column doesn't necessarily have to be land. A lot of cards in the deck (such as sol ring, Chrome Mox, a mana dork in green decks), will be perfectly suitable to make a hand keepable, though may result in losing land drops later. Subsequent turns become more muddy, and I'm not a fan of using the hypergeometric past the mulligans, since card draw effects and your curve matter more, and ramp cards can make up for land drops if necessary.
My reading from this table is that 30 is probably too low, unless the assumptions don't match your deck (if your curve is low and a 2-land hand is keepable).

40 is also probably too high, since you are mulling a hand with 5 lands in it way too often IMO.

The sweet spot IMO is a 'population' size of 34-36 or so, but for me, I'd count sol ring, and some of the other cheap ramp spells in there, since they may make a hand keepable, if a bit awkward (for example, one-lander with a sol ring into signet, or a 2-lander with a mana dork and a Cultivate, or a Ravnica bounce land and one other land). This would result in a land count in the low 30s, maybe as low as 30. Conversely, a high CMC and someone who is more risk averse may choose a population size, maybe as high as 40, but when you count Sol ring and other's that will let you keep a hand, your land count likely doesn't need to be above 35.

Land counts of 40 or more are unnecessary for securing mulligans, and excepting landfall-based decks that can play multiple lands per turn and get value off of them, land counts in the high 30s would almost certainly benefit from shaving some in favour of more draw or ramp spells. You're still going to hit your land drops, but you'll have more flexibility in the late game to draw into gas, instead of flooding out.