Have you ever wondered how much land to include in a deck? I found this chart online at gatheringmagic.com. It goes through the number of lands in a 60 card deck, then includes the average turn you should expect to hit your drops – and the turn you should get the drops with 85% certainty. There is a brief explanation of the chart at the bottom. Hope this helps!

(Source : http://www.gatheringmagic.com/magic-the-classroom-%E2%80%93-burning-pauper/)

16 total:
#1: turn one (one)
#2: turn two (four)
#3: turn three (nine)
#4: turn seven (thirteen)
#5: turn eleven (seventeen)

17 total:
#1: turn one (one)
#2: turn two (four)
#3: turn three (eight)
#4: turn six (twelve)
#5: turn ten (sixteen)

18 total:
#1: turn one (one)
#2: turn two (three)
#3: turn three (seven)
#4: turn five (eleven)
#5: turn nine (fourteen)

19 total:
#1: turn one (one)
#2: turn two (two)
#3: turn three (six)
#4: turn five (ten)
#5: turn eight (thirteen)

20 total:
#1: turn one (one)
#2: turn two (two)
#3: turn three (six)
#4: turn four (nine)
#5: turn seven (twelve)

21 total:
#1: turn one (one)
#2: turn two (two)
#3: turn three (five)
#4: turn four (eight)
#5: turn six (eleven)

22 total:
#1: turn one (one)
#2: turn two (two)
#3: turn three (four)
#4: turn four (eight)
#5: turn six (eleven)

23 total:
#1: turn one (one)
#2: turn two (two)
#3: turn three (four)
#4: turn four (seven)
#5: turn five (ten)

24 total:
#1: turn one (one)
#2: turn two (two)
#3: turn three (three)
#4: turn four (six)
#5: turn five (nine)

25 total:
#1: turn one (one)
#2: turn two (two)
#3: turn three (three)
#4: turn four (six)
#5: turn five (eight)

26 total:
#1: turn one (one)
#2: turn two (two)
#3: turn three (three)
#4: turn four (five)
#5: turn five (eight)

27 total:
#1: turn one (one)
#2: turn two (two)
#3: turn three (three)
#4: turn four (five)
#5: turn five (seven)

28 total:
#1: turn one (one)
#2: turn two (two)
#3: turn three (three)
#4: turn four (four)
#5: turn five (seven)

How this chart reads is as follows. The first number tells you how many lands you have in your deck. Under that is a list of what turn you can expect to play land #1, then #2, etc. These numbers are only on average, so I typically avoid using them. The number in parentheses is what you can expect with 85% certainty. The (numbers) are the ones I use.