Total Product vs Marginal Product
Total Product and Marginal Product are two Production & Costs concepts in AP Economics that students often mix up. Total Product is the total quantity of output produced by a firm using a given amount of inputs in a specific time period. Marginal Product is the additional output produced by adding one more unit of a variable input, holding all other inputs constant. Here is how they compare side by side.
It increases as more variable inputs, like labor, are added to fixed inputs, like capital. Initially, total product rises at an increasing rate due to specialization, then at a decreasing rate due to diminishing returns.
It is calculated as the change in total product divided by the change in the variable input. Marginal product typically rises at first due to increased efficiency, then falls due to the law of diminishing marginal returns.
Total Product vs Marginal Product: A Level and Its Slope
| Total Product | Marginal Product | |
|---|---|---|
| What one number tells you | The level of output, which is what revenue and total variable cost are built from | The direction and pace of change, which is what a hiring decision turns on |
| Units | Units of output per period | Units of output per extra worker |
| Link to the other | The running total of every marginal product so far | MP equals ΔTP ÷ ΔL, the slope of the total product curve |
| Shape as labor rises | Rises, flattens, then falls | Rises, peaks, falls through zero, then goes negative |
| Can it be negative | No, output cannot fall below zero | Yes, an extra worker can reduce total output |
| Where it peaks | At the labor quantity where marginal product equals zero | At the last worker whose contribution beats the one before, which is where diminishing returns begins |
| Cost-curve twin | Turn it on its side to read total variable cost against output | Invert it for marginal cost, since MC equals wage ÷ MP |
Read a production table across the rows, not down one column
Line up a short table and the whole relationship shows itself. With zero workers the shop makes nothing. One worker produces 14 units, two produce 32, three produce 45, four produce 52, five also produce 52, and six produce 46. Marginal product is the gap between neighbours: 14, then 18, then 13, then 7, then 0, then negative 6. Watch the third worker. Marginal product drops from 18 to 13, so diminishing marginal returns has begun, and yet total product is still climbing and will climb through one more hire. Watch the fifth worker, who adds nothing at all: total product peaks precisely where marginal product equals zero. The sixth worker gets in the way, and total product falls for the first time. Every claim worth making about this production process can be read off those two rows, which is why exam tables hand you one row and ask you to build the other.
Total product peaks where marginal product hits zero, not where it starts falling
The most reliable trap on this pair is the claim that total product falls once diminishing returns sets in. Adding less is still adding. Three distinct events get compressed into one idea by students in a hurry: marginal product begins to fall, marginal product reaches zero, and marginal product turns negative. The first marks the onset of diminishing returns and says nothing about the direction of total product. The second marks the top of the total product hill. Only the third puts the total product curve on a downward slope, and no profit-seeking firm hires there, because it would be paying a wage for output that shrinks. That third region is what a multiple choice question means when it asks which range of labor a firm would never operate in, and the answer is negative marginal product rather than diminishing marginal product. The same three landmarks explain why a firm can be well inside diminishing returns and still expanding. In the table above the sixth worker destroys output, but the fourth, hired long after returns began to diminish, still brings in seven units worth having if the wage is low enough.
Marginal product decides marginal cost, average product decides average cost
Both curves matter because a production table is a cost table in disguise. Pay each worker $84 and the marginal cost of output equals the wage divided by marginal product, so the second worker's 18 extra units cost about $4.67 each while the fourth worker's 7 extra units cost $12 each. Rising marginal cost is simply falling marginal product seen from the other side. Average product, total product divided by the number of workers, does the same job for average variable cost, which equals the wage divided by average product. One more relationship ties the two production curves together: marginal product cuts through average product at the highest point of average product, for the same reason a new score above your average pulls it up and a new score below it pulls it down. Get these links straight and a production question and a cost question become the same question wearing different clothes.
Frequently asked questions
How do you calculate marginal product from a total product table?
Marginal product equals the change in total product divided by the change in the variable input. Subtract the previous row's total product from the current row, then divide by the number of workers added, which is usually one, so the subtraction alone gives the answer. Write each result between two rows rather than on one, because marginal product describes a move from one input level to the next. A negative result is legitimate and simply means the extra worker reduced total output.
Can marginal product be falling while total product is rising?
Falling marginal product alongside rising total product is the normal situation, and it defines the range where a firm actually operates. Each additional worker contributes less than the worker hired before, but as long as that contribution stays above zero, total output keeps climbing. Total product only stops rising when marginal product reaches zero. A firm deciding how many workers to hire compares the value of that shrinking contribution with the wage, and stops where the two meet rather than where marginal product first dips.
What is the difference between marginal product and average product?
Marginal product measures output added by one more worker, while average product measures output per worker across the whole workforce, total product divided by labor. The two move together but not identically. Average product rises while marginal product sits above it and falls once marginal product drops below it, so the marginal curve crosses the average curve at the average curve's peak. On the cost side, average product connects to average variable cost while marginal product connects to marginal cost.
Live Production Costs graph. Drag the curves, or open the full version.
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