How many power moons are there?

Let's get more specific. There are far more moons available in many levels since there are multi-moons (counts as 3 power moons). Also most kingdoms have Crazy Cap stores so you can potentially get many more in that world. Here's a more detailed breakdown:

• Mushroom Kingdom + Crazy Cap Store

  Listed      Regular     Multi       Toadette    Total
  104         37           6x3=18     61          +116
  

• Cap Kingdom + Crazy Cap Store

  Listed      Regular     Multi       Endgame     Total
  31          17           0x3= 0     14          +31
  

• Cascade Kingdom + Crazy Cap Store

  Listed      Regular     Multi       Endgame     Total
  40          24           1x3= 3     15          +42
  

• Sand Kingdom + Crazy Cap Store

  Listed      Regular     Multi       Endgame     Total
  89          67           2x3= 6     20          +93
  

• Lake Kingdom + Crazy Cap Store

  Listed      Regular     Multi       Endgame     Total
  42          32           1x3= 3     9           +44
  

• Wooded Kingdom + Crazy Cap Store

  Listed      Regular     Multi       Endgame     Total
  76          52           2x3= 6     22          +80
  

• Cloud Kingdom

  Listed      Regular     Multi       Endgame     Total
  9           2            0x3= 0     7           9
  

• Lost Kingdom + Crazy Cap Store

  Listed      Regular     Multi       Endgame     Total
  35          25           0x3= 0     10          +35
  

• Metro Kingdom + Crazy Cap Store

  Listed      Regular     Multi       Endgame     Total
  81          64           2x3= 6     15          +85
  

• Snow Kingdom + Crazy Cap Store

  Listed      Regular     Multi       Endgame     Total
  55          36           1x3= 3     18          +57
  

• Seaside Kingdom + Crazy Cap Store

  Listed      Regular     Multi       Endgame     Total
  71          51           1x3= 3     19          +73
  

• Luncheon Kingdom + Crazy Cap Store

  Listed      Regular     Multi       Endgame     Total
  68          54           2x3= 6     12          +72
  

• Ruined Kingdom

  Listed      Regular     Multi       Endgame     Total
  10          4            1x3= 3     5           12
  

• Bowser's Kingdom + Crazy Cap Store

  Listed      Regular     Multi       Endgame     Total
  62          44           1x3= 3     17          +64
  

• Moon Kingdom + Crazy Cap Store

  Listed      Regular     Multi       Endgame     Total
  38          27           0x3= 0     11          +38
  

• Dark Side

  Listed      Regular     Multi       Endgame     Total
  24          23           1x3= 3     0           26
  

• Darker Side

  Listed      Regular     Multi       Endgame     Total
  1           0            1x3= 3     0           3
  

• Grand Total

                                      Toadette
  Listed      Regular     Multi       /Endgame    Total
  836         559         22x3=66     255         +880
  

That brings it down to a grand total of 836 listed moons, and counting multi-moons, 880 power moons found in the world. Then if you want to get the max of 999, you'll need to buy at least 119 additional moons from Crazy Cap Stores.

According to the Prima Guide:

• Cap Kingdom: 31 moons
• Cascade Kingdom: 40
• Sand Kingdom: 89
• Lake Kingdom: 42
• Wooded Kingdom: 76
• Cloud Kingdom: 9
• Lost Kingdom: 35
• Metro Kingdom: 81
• Snow Kingdom: 55
• Seaside Kingdom: 71
• Luncheon Kingdom: 68
• Ruined Kingdom: 10
• Bowser's Kingdom: 62
• Moon Kingdom: 38
• Mushroom Kingdom: 43 (becomes 104 for achievements)
• Dark Side: 24
• Darker Side: 1

The above adds up to 836.

NB: Multi-moons count as a single moon in these numbers, because it is based on the row in the map's list, which marks multi-moons as a single row with a "3" beside it.

$ CAP KINGDOM POWER MOONS

Number of Power Moons: 31

Additional info: None are available at the start of the game, but you can collect them after revisiting it following your journey to Cascade Kingdom. Some Power Moons can only be obtained after defeating Bowser.

$ CASCADE KINGDOM POWER MOONS

Number of Power Moons: 40

$ SAND KINGDOM POWER MOONS

Number of Power Moons: 89

Additional info: There are only 69 Power Moons prior to Bowser being defeated.

$ LAKE KINGDOM POWER MOONS

Number of Power Moons: 42

$ WOODED KINGDOM POWER MOONS

Number of Power Moons: 76

Additional info: There are only 54 Power Moons prior to Bowser being defeated.

$ CLOUD KINGDOM POWER MOONS

Number of Power Moons: 9

Additional info: Every Power Moon can only be obtained after revisiting Cloud Kingdom after defeating Bowser.

$ LOST KINGDOM POWER MOONS

Number of Power Moons: 35

$ METRO KINGDOM POWER MOONS

Number of Power Moons: 81

$ SNOW KINGDOM POWER MOONS

Number of Power Moons: 55

$ SEASIDE KINGDOM POWER MOONS

Number of Power Moons: 71

$ LUNCHEON KINGDOM POWER MOONS

Number of Power Moons: 68

$ RUINED KINGDOM POWER MOONS

Number of Power Moons: 10

$ BOWSER'S KINGDOM POWER MOONS

Number of Power Moons: 62

$ MOON KINGDOM POWER MOONS

Number of Power Moons: 38

Additional info: Mario doesn't need to collect any Power Moons on Moon Kingdom to progress through the story.

$ MUSHROOM KINGDOM POWER MOONS

Number of Power Moons: 61

Additional info: There are 43 Power Moons to pick up across the Mushroom Kingdom, and an additional 61 you receive by cataloguing your achievements with Archivist Toadette.

$ DARK SIDE POWER MOONS

Number of Power Moons: 24

$ DARKER SIDE POWER MOONS

Number of Power Moons: 1