I just did a massive landscaping project in my front yard and ran into this exact same issue. The tricky part is that bag sizes at Home Depot (usually 2 cu ft) don't easily translate to the square footage of a curved garden bed, so you usually end up making three trips to the store.

A good rule of thumb is that if you want a standard 3-inch depth to block weeds, one 2-cubic-foot bag will only cover about 8 square feet. If you have weird shaped beds, I highly recommend using this type of mulch calculator: https://easyhomecalc.com/calculators/mulch-calculator.html. You just plug in your measurements and it tells you exactly how many bags so you need to buy so you don't overspend.