what is the difference between first class and priority mail comes down to delivery speed, weight limits, and pricing. USPS First-Class Mail is intended for lightweight items (under 16 oz) and is generally cheaper, but delivery takes 2-5 business days. Priority Mail supports heavier items (up to 70 lbs) and delivers faster—typically within 1-3 business days. Priority Mail also includes tracking and $100 insurance, whereas First-Class only includes tracking without insurance. For valuable or time-sensitive shipments, Priority Mail is the preferred option. Businesses often choose between these services based on item weight, urgency, and cost considerations.