Gather all ingredients. Preheat the oven to 300 degrees F (150 degrees C).
Bring water to a boil in a medium pot; stir in rice. Reduce heat to medium-low, cover, and simmer until rice is tender and water has been absorbed, 20 to 25 minutes.
Mix rice vinegar, sugar, and salt in a small bowl. Gently stir into cooked rice in the pot and set aside.
Lay nori sheets on a baking sheet.
Heat nori in the preheated oven until warm, 1 to 2 minutes.
Center 1 nori sheet on a bamboo sushi mat. Use wet hands to spread a thin layer of rice on top. Arrange 1/4 of the crabmeat, avocado, cucumber, and pickled ginger over rice in a line down the center.
Lift one end of the mat and roll it tightly over filling to make a complete roll. Repeat with remaining ingredients.
Use a wet, sharp knife to cut each roll into 4 to 6 slices.
