Total, average and marginal product

A teaching model — not a real plant’s production function; units are notional.

Labour L (capital fixed)
10
Total TP · marginal MP · average AP140 MP 19 · AP 14

Diminishing marginal product — the addition shrinks but is still positive, so total output keeps rising

Each extra unit of labour adds some output (marginal product). At first the addition grows, then it shrinks; while still positive, total output keeps rising. Marginal product pulls the average up when above it and down when below, so they meet at the top of the average.

0100200300Total product TPinflectionTP max -40-20020051015202530Labour L★

Tangent (slope = MP) Ray (slope = AP) MP AP ★ MP = AP (top of AP)

Bands: increasing diminishing (TP still rising) MP < 0 (TP falling)

Model assumption: TP = 4L + 1.5L² − 0.05L³. The curve shapes and diminishing returns are in the study guide; the cubic and "MP crosses the top of AP" are learning supplements. Diminishing marginal product (labour only, short run) is not decreasing returns to scale (all inputs, long run).

Not in this calculation

  • Shifting the whole curve by changing capital (long run)
  • Changing two inputs together — see the isoquant tool
  • Costs — turning marginal product into marginal cost
  • Wages and prices
  • Any real plant’s input–output curve

Using the example values

Tool: Renuary (CC BY 4.0) · Numbers are examples. Method and limits on the original page.