Identify how celery flakes are used: dry seasoning/rub (most common), or baked-in flavor where texture can matter.
Choose the closest match from the table: celery seed for maximum similarity, dried celery for aroma/texture, celery salt if you can reduce recipe salt.
Apply using the listed ratio; if your swap is wetter (fresh celery) or saltier (celery salt), scale down to prevent overpowering.
Adjust after the first taste: add a pinch more herb to boost, or cut back and rebalance salt/sweetness if the profile shifts.