Cost Per Unit

How to calculate cost per unit

Variable costs rise with output: materials, direct labor paid per piece, packaging, freight on each order. Fixed costs stay the same across the volume range you're working in: rent, supervisors, equipment leases, insurance. Add both, then divide by the number of units.

The answer depends on which costs you include, and there are three common versions. Manufacturing cost per unit counts only production costs, and it is what goes into inventory on the balance sheet. Variable cost per unit counts only costs that change with each unit, which is the number for volume and one-off pricing decisions. Fully loaded cost per unit adds selling, shipping and administrative costs, and it is the one that has to be recovered for a price to make money.

Worked example: a small manufacturer

A company started 10,000 units in a quarter and 9,600 passed inspection, a scrap rate of 4%. Variable manufacturing costs were $110,000 (materials, direct labor, variable overhead), and fixed manufacturing overhead was $48,000. Selling, shipping and administrative costs were $43,100.

Manufacturing cost is $16.46, and the fully loaded cost is $20.95. At a $29.00 price, profit per unit is $8.05, which is a 27.8% margin on price. The contribution margin, price minus the $11.46 variable manufacturing cost (ignoring variable selling costs here), shows what each sale adds toward fixed costs. Compare it with the contribution margin definition when you need the per-unit view.

Note what dividing by the wrong number does. Using the 10,000 units started gives $158,000 ÷ 10,000 = $15.80. That understates the true cost by $0.66 a unit because it treats the 400 scrapped units as if they could be sold.

Why cost per unit falls as volume rises

Fixed costs don't change with output, so more units share them. Variable cost per unit stays about the same. In the example, watch the fixed part shrink while the variable part holds.

Doubling volume from the half level to the base level takes $5.00 off each unit. Moving from the base to 1.5 times gets only $1.67 more. The savings shrink as fixed cost gets thinner, and they hold only within a relevant range. Add a second shift or another machine and fixed costs step up, which raises the unit cost again until the new capacity fills. See how this feeds the break-even point.

Allocating shared costs across products

When a plant makes more than one product, shared fixed costs have to be split, and the split changes each product's cost. Suppose product A has $8 of variable cost and product B has $20. The company makes 8,000 units of A, which take half an hour each, and 2,000 of B, which take two hours each. Shared fixed overhead is $48,000.

By units, both products carry $4.80 of overhead. By labor hours (8,000 hours in total), A carries $3.00 and B carries $12.00. Product B's cost jumps from $24.80 to $32.00 without any real change in the business. Pick the base that reflects what actually consumes the overhead, and use the same base every period. The absorption costing and predetermined overhead rate entries cover the method in more detail.

Using cost per unit for pricing decisions

The right cost depends on the decision. For a long-term price list, use the fully loaded cost, because a price below it doesn't recover overhead. Here that is $20.95, so a $29.00 price leaves $8.05 of profit.

For a one-time order when capacity would otherwise be idle, the relevant cost is the marginal cost, which in the short run is mostly variable cost. A special order at $15.00 is below fully loaded cost but above the $11.46 variable manufacturing cost, so it adds about $3.54 a unit to profit if it doesn't displace a full-price sale or set a precedent. The risk is doing this so often that no order ever pays for the fixed costs. Use cost-plus pricing and the markup vs margin calculator to turn a cost into a price.

Four ways to lower cost per unit

• Raise volume. Spread the same fixed costs over more units. It only helps if you can sell the extra units at the same price.
• Reduce scrap. Cutting scrap from 4% to 2% means 9,800 good units from the same 10,000 started. At $158,000, cost per unit falls from $16.46 to $16.12.
• Cut input prices. Renegotiate materials or shift suppliers. Materials are often the largest variable cost, so a 5% reduction there has a direct effect.
• Improve labor efficiency. Fewer minutes per unit lowers the variable labor cost, and it frees capacity that can be sold.

Run these through the cost per unit calculator to see which lever moves your number most, since the effect of each one varies with your cost structure.

Common mistakes

• Dividing by units started instead of good units. In the example this understates cost by $0.66 per unit, and it hides the scrap problem.
• Using last year's volume for this year's fixed-cost spread. If volume drops 30%, cost per unit rises even though nothing changed in the plant. Recompute for the volume you expect.
• Mixing periods. Monthly fixed costs divided by quarterly output produce a meaningless figure.
• Including costs that don't belong to the product. Interest and one-off legal settlements are not part of unit cost.
• Charging idle capacity to the units that were made. Unused capacity is a cost of the period, and spreading it over fewer units overstates each one.
• Using a single number for every decision. Use fully loaded cost for price lists, and marginal cost for special orders and make-or-buy choices.

What cost per unit can't tell you

Cost per unit is an average. It says nothing about the cost of the next unit, and it moves with volume, so a figure from one quarter shouldn't be assumed for the next. It also depends on allocation choices, as the two-product example shows. Treat it as a planning number, pair it with fixed costs and margin analysis, and compare the actual result with a standard cost to see where the variances come from.

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