Non-canon, hypothetical and forms with vague showings are put in-between the real list.

Bankai

8. Ichigo

Visored Bankai

7. Ichigo

Hollow mask

Possessed

6.5 Ichigo

Fullbring Bankai

6. Ichigo

Ichigo's second Bankai

Vasto Lorde

5. Ichigo

Full Hollow form

Skull Clad

4.5 Ichigo

Dangai

4. Ichigo

Mugetsu

3. Ichigo

Final Getsuga Tensho

True Shikai

3. Ichigo

True Shikai Hollow Merged

2. Ichigo

True Bankai

1.5 Ichigo

True Bankai Hollow Merged

1. Ichigo

What is commonly referred to as the "End of Series" form.

Adult

0. Ichigo