Marginal product (MP) is the additional output produced by adding one more unit of an input (usually labor) while holding all other inputs constant. In AP Micro, MP = change in total product ÷ change in input, and it typically falls as you add more of an input because of diminishing marginal returns.
Marginal product answers one question: if a firm hires one more worker (or adds one more machine), how much extra output does it get? You calculate it as the change in total product divided by the change in the input. So if 4 workers make 100 pizzas and 5 workers make 115, the marginal product of the 5th worker is 15 pizzas.
The pattern matters as much as the number. In the short run, at least one input (like the kitchen or factory) is fixed. Early workers might specialize and boost MP, but eventually each new worker adds less and less because they're crowding around the same fixed equipment. That's diminishing marginal returns (EK PRD-1.A.3), and it's the reason the total product curve flattens out and, on the cost side, why marginal cost eventually rises. Marginal product, average product, and total product all shift together as input usage changes (EK PRD-1.A.2), so a table of labor and output should let you compute all three.
Marginal product is the hinge between two units. In Topic 3.1 (The Production Function), it's the core productivity measure behind learning objectives AP Micro 3.1.A and 3.1.C, where you define, graph, and calculate MP from a table. Falling MP is what makes the marginal cost curve slope upward, which is the foundation for everything else in Unit 3, from cost curves to the perfect competition model.
Then in Topic 5.1 (Introduction to Factor Markets), marginal product gets a price tag. Multiply MP by the price of the output and you get marginal revenue product, which firms compare to the wage to decide how many workers to hire (AP Micro 5.1.C, EK PRD-4.A.1). Diminishing MP is also why the labor demand curve slopes downward. If you don't have MP locked down, both the cost-curve questions in Unit 3 and the hiring questions in Unit 5 fall apart.
Keep studying AP Microeconomics Unit 3
Diminishing Marginal Returns (Unit 3)
Diminishing marginal returns is just the story of what happens to MP in the short run. As a firm piles more workers onto a fixed amount of capital, each new worker's marginal product shrinks. Same concept, viewed as a trend instead of a single number.
Total Product (Unit 3)
Marginal product is the slope of the total product curve. When MP is positive, TP rises; when MP falls but stays positive, TP rises at a slower rate; if MP ever turns negative, TP actually drops. Reading one curve tells you the shape of the other.
Demand for Labor (Unit 5)
A firm's labor demand curve is its marginal revenue product curve, which is just MP × output price. Because MP diminishes, MRP falls as more workers are hired, and that's exactly why the demand for labor slopes downward.
Derived Demand (Unit 5)
Firms don't want workers for their own sake; they want the output workers produce. Marginal product is the measurement that makes derived demand concrete, since it tells the firm precisely how much product each additional worker is worth hiring for.
Multiple-choice questions hand you a table of labor and total product and ask you to compute marginal product, identify where diminishing marginal returns set in, or connect falling MP to rising marginal cost. Fiveable practice questions hit the same angles, including what MP means within the production function and what a firm weighs when deciding how much labor to hire.
On FRQs, marginal product usually shows up wearing its Unit 5 outfit. The 2017 FRQ Q2 gave a table of output at different amounts of capital and labor in perfectly competitive factor markets and asked for hiring decisions, which means computing MP, converting it to MRP, and comparing it to the factor price. The move you must be able to make is mechanical: MP = ΔTP/ΔL, then MRP = MP × P, then hire as long as MRP ≥ wage. Show the calculation, not just the answer.
Marginal product is measured in units of output (the 5th worker adds 15 pizzas). Marginal revenue product is measured in dollars (those 15 pizzas at $10 each mean an MRP of $150). MP is a physical productivity concept from Unit 3; MRP attaches the output price so the firm can compare it to the wage in Unit 5. Firms hire based on MRP versus the wage, not MP alone, because a worker's productivity only matters in dollar terms.
Marginal product is the change in total product divided by the change in an input, holding all other inputs constant.
In the short run, marginal product eventually falls as more of a variable input is added to a fixed input, which is the law of diminishing marginal returns.
Marginal product is the slope of the total product curve, so when MP falls, total product still rises but at a slower rate.
Falling marginal product is the direct reason marginal cost rises, linking the production function to the cost curves in Unit 3.
Multiply marginal product by the output price to get marginal revenue product, which firms compare to the wage to decide how many workers to hire in Unit 5.
On FRQs like 2017 Q2, you compute MP from a table first, then convert it to MRP to answer the hiring question.
Marginal product is the extra output a firm gets from adding one more unit of an input (usually one more worker) while keeping other inputs fixed. You calculate it as the change in total product divided by the change in the input, so if output rises from 100 to 115 when a 5th worker is hired, MP = 15.
No. Marginal product is measured in units of output, while marginal revenue product is MP multiplied by the output price, measured in dollars. Firms compare MRP (not MP) to the wage when deciding how many workers to hire.
No. As long as MP is positive, total product is still increasing, just at a slower rate. Total product only falls if marginal product becomes negative, which happens when extra workers actually get in each other's way.
In the short run, at least one input like capital is fixed. As more workers share the same fixed equipment and space, each additional worker contributes less extra output, so MP falls (EK PRD-1.A.3).
Marginal product measures the output of the last unit of input added, while average product is total output divided by the total number of input units. MP pulls AP toward it, so AP rises when MP is above it and falls when MP is below it.