Costs and Economies of Scale

Accountants and economists calculate profit differently; many suppliers experience economies of scale as output expands, which implies that long-run average total costs are falling. At very high levels of production, however, many firms are likely to experience diseconomies of scale.

What is the difference between how accountants and economists calculate profit giving example of costs each might use in this calculation?

Why do firms experience diseconomies of scale as they increase production volume?

How might firms "avoid" experiencing diseconomies of scale?