How many power moons are there?

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.

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.