To cook salmon at 400°F, the general guideline is:

• For a 4-ounce fillet (about 1 inch thick), bake for 10 to 15 minutes.
• Thicker fillets (more than 1 inch) usually take 15 to 20 minutes.
• Thin fillets (about ½ inch thick) take around 8 to 10 minutes.
• The salmon is done when its internal temperature reaches 130-135°F for a moist, tender texture, although the FDA recommends 145°F for safety.
• Let the salmon rest for 5 to 10 minutes after baking to allow juices to reabsorb.

These times ensure the salmon cooks through without drying out and can vary slightly based on thickness, starting temperature, and desired doneness.