Isocost Curves – Cost Combinations for Inputs

While isoquants show equal output combinations, isocost lines show equal cost combinations of inputs.

1. Meaning of Isocost Line

Isocost line shows all possible combinations of two inputs (labour and capital) which can be purchased with a given total cost at given factor prices.

Assume:

• Wage rate of labour = w
• Rental price of capital = r
• Total cost = C

Then isocost equation:

C = wL + rK

Where L = units of labour, K = units of capital.

2. Shape of Isocost Line

• Straight line sloping downwards from left to right.
• When firm uses more labour (L), it must use less capital (K) to keep total cost constant.

3. Shifts in Isocost Line

(a) Change in Total Cost (C)

• If total cost increases, with same input prices → isocost line shifts upwards (right) (parallel shift).
• If total cost decreases, line shifts downwards (left).

(b) Change in Factor Prices (w or r)

• If wage rate (w) falls while r and C constant → firm can hire more labour → isocost line pivots.
• Similarly for change in rental price of capital.

4. Isocost Map

• Set of isocost lines for different total cost levels.
• Higher isocost line → higher total cost.

5. Quick Revision Points

• Isocost line: C = wL + rK, combinations of L and K with same cost.
• Downward straight line; shifts with change in total cost or factor prices.
• Used together with isoquants to find producer’s equilibrium.

6. Quiz Time 🎯