Cost, Price, Margin
Unit economics is the money one sale leaves behind: price minus the cost of making and delivering that unit equals its contribution margin. · 11 min
A sale sounds like good news until you ask a plain question: how much did that one sale actually leave you? Not the price on the tag — the money left over after you paid to make the thing and put it in the buyer's hands. That leftover is what a business runs on. Unit economics is just the arithmetic of a single sale: take the price, subtract the cost of making and delivering that one unit, and what remains is the margin the sale contributes. Get this number right for one unit and you can reason about a thousand.
Guess before you learn
You sell a candle for $20. The wax, wick, and jar cost $6, and packaging plus shipping cost $4. How much does one sale leave behind?
The unit costs $6 to make and $4 to deliver — $10 in all. Price $20 minus that $10 unit cost leaves $10. If you picked $14, you counted only the making and forgot delivery — one of the most common and expensive mistakes. Delivery is part of the cost of the sale.
9–12
3–5
Every sale has two numbers hiding inside it. One is the price, what the buyer pays. The other is the cost, what you spent to make and hand over that one thing. The difference between them is the margin — the money the sale actually leaves you. A high price with an even higher cost can leave almost nothing.
6–8
Unit cost is everything you spend to make and deliver one unit — materials, packaging, shipping, any per-sale fee. Contribution margin is the price minus that unit cost: the money one sale contributes. Written plainly: margin = price − unit cost.
It is called a contribution because that leftover contributes to the costs that do not change per sale — rent, tools, your time — and only after those are covered does anything become profit. This is why price alone tells you little. A $50 sale that costs you $48 to fulfill contributes $2; a $10 sale that costs $3 contributes $7.
9–12
Separate two kinds of cost. Variable costs rise with each unit — materials, shipping, transaction fees — and belong in the unit cost. Fixed costs stay roughly the same whether you sell one unit or a hundred — rent, equipment, a subscription. Contribution margin, price minus variable unit cost, is what each sale gives you toward those fixed costs and, eventually, profit.
Margin as a percentage — margin divided by price — lets you compare offers of different sizes. A 50% margin means half of every dollar the buyer pays stays with you to cover fixed costs. A thin margin is not fatal, but it demands high volume; a fat margin forgives a slower start.
K–2
You sell a cup of lemonade for four coins. The lemons and cup cost you one coin. So each cup leaves you three coins. That leftover is your margin. Price take away cost is what you keep.
Undergrad
Unit economics isolates the marginal transaction. Contribution margin per unit equals price minus variable cost per unit; contribution margin ratio is that figure over price. The word contribution is precise: each sale contributes its margin toward fixed costs, and total profit is total contribution minus total fixed cost. This decomposition is what makes break-even and scaling tractable — questions the next folio takes up.
The discipline early on is honesty about what is variable. Payment-processing fees, returns, and the free replacement you send when one arrives broken are all real per-unit costs, and founders routinely omit them. A margin computed on materials alone flatters the business and hides the moment when volume makes a thin-margin unit a liability rather than a win.
Postgrad
Let p be price and v the variable cost per unit; contribution margin is m = p − v and the ratio is m/p. Over a horizon, profit is π = (p − v)·q − F, with q units and F fixed cost. Unit economics is the study of m before q and F enter, because a nonpositive m means no quantity redeems the venture: scaling a unit that loses money loses money faster.
The subtlety is boundary-drawing between v and F, which is horizon-dependent: labor is fixed weekly but variable annually; capacity steps are fixed until a threshold then jump. For first-sale reasoning, charge to v every cost that genuinely moves with the unit — including expected returns, support, and processing — so m reflects the true contribution rather than an accounting convenience.
contribution margin
The money one sale leaves after its own costs: margin = price − unit cost. Plain descriptor: what a single sale contributes toward the rest of the business.
Why is this true?
Why can a higher-priced sale leave less behind than a cheaper one?
Because margin is price minus the unit's own cost, not the price itself. A $50 sale that costs $48 to make and deliver leaves $2, while a $10 sale that costs $3 leaves $7. The cost of the unit, not the size of the price, decides what a sale contributes.
Find the contribution margin on one candle — the steps fade as you master them
3 + 1 + 2 = 6
1 + 3 = 4
6 + 4 = 10
20 − 10 = 10
10 ÷ 20 = 0.5
Two habits keep this number honest. First, count every per-unit cost, not just the obvious ones: packaging, shipping, the fee the payment app takes, the occasional refund or broken replacement. A margin figured on materials alone always flatters you. Second, watch the margin, not the price, when you judge whether a sale is worth making. A thin margin is not always wrong, but it means you need many sales to add up to anything, and it leaves no room for the surprise costs that always come. A healthy margin forgives a slow start; a thin one punishes it.
Practice — new ink and old, interleaved
1.You have proven one narrow channel brings steady customers. When should you add a second?
2.When founders overstate their margin, the most common reason is:
3.A warm referral is standing in front of you. You have named the price. What do you do?
4.Which is the honest first-year market estimate?
5.Which is the strongest sign a problem is worth solving?
6.Name the three signs a problem is worth paying to solve.
People already spend money on a poor fix, lose time to it, or build a workaround.
How close were you? Grade yourself honestly — it sets your review date.
7.Your unit cost is $16 and you want to keep $20 per sale. What price is that?
8.In one sentence, name the three kinds of evidence that a problem is real.
9.A bag sells for $45. Materials cost $16, and packaging plus shipping cost $9. What is the contribution margin?