The labor market is the first market most students meet where the price is a wage and the good being traded is a worker's time. The mechanics are the same supply-and-demand machine as a product market, but with one crucial twist on the demand side: a firm's demand for labor is derived from the demand for its output. This guide builds the labor market up from labor supply, labor demand, and the marginal revenue product of labor, then finds the equilibrium wage.
Labor Demand Comes From the Output the Worker Makes
Firms don't want workers for their own sake. They want the output those workers produce. So a firm's demand for labor is a derived demand — it depends on the price of the firm's product and how much extra output an additional worker produces.
The standard measure is the marginal revenue product of labor (MRP_L): the extra revenue the firm gets from hiring one more worker.
MRP_L = MP_L × P
where MP_L is the marginal product of labor (the extra physical output one more worker produces) and P is the price the firm receives per unit of output. In a competitive output market, P is the market price; in an imperfectly competitive market, MRP_L uses marginal revenue rather than price, but the spirit is the same.
The firm hires up to the point where the extra revenue from the next worker equals the cost of hiring that worker. In a competitive labor market, the cost of one more worker is the wage (W), so the firm's hiring rule is:
Hire one more worker if MRP_L > W; stop when MRP_L = W.
That equation traces out the firm's labor demand curve: it is the MRP_L curve itself, which slopes down because of diminishing marginal product (each additional worker eventually adds less than the one before).
Labor Supply Comes From Workers' Trade-Off
The labor supply curve to a firm — and to the whole market — generally slopes up: as the wage rises, more people are willing to work, and existing workers are willing to put in more hours. The trade-off behind it is the classic work vs. leisure decision. A higher wage makes leisure more expensive (the substitution effect, which pushes toward more work) and makes the worker richer at every hour worked (the income effect, which pushes toward less work). For most workers across most wages, substitution dominates, so labor supply slopes up.
A single competitive firm hiring in a much larger market faces a horizontal labor supply curve at the going market wage — it can hire any number of workers at that wage and none below it. The market-level labor supply curve is the usual upward-sloping one.
Equilibrium Wage and Quantity
Equilibrium in the labor market is where the market labor supply curve crosses the market labor demand curve. The wage at that crossing is the equilibrium wage W; the quantity is the equilibrium employment L. Any wage above W generates a labor surplus (unemployment at that wage); any wage below W generates a labor shortage.
Worked example. A small café faces these MP_L numbers and sells coffee at $4 per cup:
- 1st barista: 30 cups/hour → MRP_L = 30 × $4 = $120/hour
- 2nd barista: 25 cups/hour → MRP_L = $100/hour
- 3rd barista: 18 cups/hour → MRP_L = $72/hour
- 4th barista: 10 cups/hour → MRP_L = $40/hour
- 5th barista: 4 cups/hour → MRP_L = $16/hour
If the market wage for baristas is $50/hour, the café hires every barista whose MRP_L ≥ $50: that's the first three. The 4th barista would add $40 in revenue at a $40 cost gap — not worth it. So this firm's labor demand at W = $50 is 3 workers.
Repeat that hiring rule across every firm in the market, sum the quantities, and you have the market labor demand at each wage. Cross it with the upward-sloping market labor supply and you have W and L.
What Shifts Each Curve
A few standard movers, distinct from movements along either curve.
Labor demand (MRP_L) shifts because of:
- A change in the output price. Coffee prices double → MRP_L doubles at every L → demand for baristas shifts right.
- A change in productivity. A better espresso machine raises MP_L → MRP_L rises → demand shifts right.
- A change in the price of substitute or complementary inputs. Cheaper self-serve kiosks substitute for baristas, shifting labor demand left.
Labor supply shifts because of:
- Population and labor-force participation. More people in the area → supply right.
- The wage in alternative jobs. If fast-food wages rise, the supply of workers willing to be baristas at any given wage falls.
- Non-wage factors. Better hours, benefits, or job satisfaction raise supply at every wage.
A minimum wage above W* acts as a binding price floor in this market — the same mechanics as any other binding floor: a labor surplus (i.e., unemployment among workers seeking jobs at that wage). For the general anatomy of binding price floors and ceilings, see price floors vs. price ceilings.
Conclusion
Labor market basics start with one rule: a firm hires labor up to the point where MRP_L equals the wage. Labor demand is derived from product demand and slopes down because of diminishing marginal product; labor supply slopes up because workers trade leisure for wages. Cross the two curves and you have the equilibrium wage and employment level — and the same supply-and-demand tools that handle any other market handle this one too.
