Two totals at your volume, the cheaper one, and the break-even volume where the cost lines cross. The delivery fee is the variable that pivots the decision — most "mulch calculators" omit it.

1 yd³ = 27 ft³

volume (Area + depth mode):
  volume_yd3 = area_ft² × (depth_in / 12) / 27

bagged:
  bags_needed  = ceil(volume_yd3 × 27 / bag_size_ft³)   ← rounded up to whole bags
  bagged_total = bags_needed × price_per_bag

bulk:
  bulk_total = volume_yd3 × price_per_yd3 + delivery_fee

break-even (continuous-bag approximation):
  effective_bag_$/yd³ = (27 / bag_size_ft³) × price_per_bag
  breakeven_yd3       = delivery_fee / (effective_bag_$/yd³ − price_per_yd3)

winner = lower of (bulk_total, bagged_total); savings = |difference|

Worked example: bag 2 ft³ @ $3.97, bulk $38/yd³, delivery $50 → effective bag rate $53.60/yd³, break-even ≈ 3.2 yd³. At 2 yd³ bagged wins ($107.19 vs $126.00); at 5 yd³ bulk wins ($240.00 vs $269.96).

The bagged total uses the real rounded-up bag count (a true purchase), while the break-even uses a smooth continuous-bag line so it lands on one clean rule-of-thumb figure. When the bulk per-yard rate never beats the per-bag rate, there is no positive crossover and bagged wins at every volume. Prices shown are illustrative placeholders, not sourced market rates.

Formula: break-even yd³ = delivery_fee / ((27 / bag_ft³) × bag_price − bulk_$/yd³)

See Sources below