How many tallies does Toko Fukawa have on her leg exactly? Here's 2 pictures I have of her showing her tallies!
The answer is: there's no exact number, the tally marks changed from one to other titles.

For reference, this is how the Japanese tally marks work for 1 to 5:


  


Ignoring the fan arts since there are too many variants,


Danganronpa: Trigger Happy Havoc



Probably 32. It seems she wrote the mark from top-to-bottom (from her POV), thus finishing the first row of 20 (4x5). Continuing to the bottom row, there are 3 visible characters. Assuming she wrote it from left-to-right, the first 2 characters should have finished, making them 10 (2x5). The last character seems to stop at 2.
Danganronpa: The Animation (correspond to DR: Trigger Happy Havoc)



At least 30. The visible tally marks are in form of 2 rows of 3 characters, and all of them are complete, making them 30 (2x3x5).
Danganronpa Another Episode: Ultra Despair Girls



The 3D model only shows 4 characters and in the same pattern with DR1 with the last character stops at 2. Since the rest are probably hidden by her skirt, at least 17 (+ multiple of 5), or possibly 32 (same as DR1).



However, her in-game artwork shows different tally marks. There area 3 rows of 3 characters instead. The bottom-middle character seems to be the last character and stops at 2. It's probably 37 (7x5 + 2).
Cyber Danganronpa VR: The Class Trial (correspond to DR: Trigger Happy Havoc)

(Caution: probably NSFW, panty image)


   


Probably 27 or 37. The visible tally marks are in form of 2 rows of 3 characters, while the last character stops at 2. There might be another pair hidden behind her thigh, making the total to 37.
Divine Gate (collaboration)



Probably 37. The visible tally marks are in form of 2 rows of 4 characters (the first pair is hidden in the shadow), and the last character stops at 2.


Conclusion

The tally marks are between 17-37, with 32 &amp; 37 as possible answers. However, one certain thing is, the last character stops at 2.