Unit Economics and Contribution Margin

“The margins are fine, but the unit economics don’t work.” It’s a sentence that sinks funding pitches and kills product lines, and it sounds intimidating. It isn’t. Unit economics just zooms all the way in to a single sale and asks the most basic question in business: does this one transaction make money once you strip out everything that isn’t tied to it? We’ll answer it for Foundry Manufacturing, our precision-parts maker, one part at a time. The tool is contribution margin, and it rests on one distinction you already half-know.

Fixed vs variable costs

Every cost Foundry has falls into one of two buckets:

• Variable costs rise and fall with each part you make and sell. Make one more part and these go up: the steel and materials, the machine time, packing and shipping that unit.
• Fixed costs stay roughly the same no matter how much you sell: the factory rent, salaried staff, the core software, the front office. Sell zero parts or a million — the rent is the rent.

This split is the whole foundation of unit economics. Variable costs belong to the part; fixed costs belong to the business. Foundry’s $6M of product costs behave like variable costs (they scale with how many parts it ships), and its $3M of operating expenses behave like fixed costs.

Contribution margin: what one sale leaves behind

Contribution margin is the price of one unit minus the variable cost of that unit:

contribution margin = price − variable cost per unit

Foundry sells a typical part for $100 and it costs $60 in materials, machine time, and shipping, so each part contributes $40 — a 40% contribution margin. That’s no coincidence: it mirrors Foundry’s 40% gross margin at the company level ($10M revenue, $6M product cost, $4M gross profit). The per-unit view and the whole-company view are the same 60/40 split seen from different distances.

That $40 doesn’t all become profit — first it goes toward covering the fixed costs (factory rent, salaries). Only once all the fixed costs are covered does contribution turn into profit. That crossover point is Foundry’s break-even: fixed costs of $3M ÷ $40 per part = 75,000 parts. Foundry actually sells about 100,000 parts ($10M ÷ $100), so it clears break-even with room to spare — 100,000 × $40 = $4M of contribution, minus $3M of fixed costs, leaves $1M of operating profit. We work through this break-even math in Fixed Costs, Variable Costs and Break-Even.

So “good unit economics” means the contribution margin is healthily positive and you can sell enough units to clear your fixed costs comfortably. “Bad unit economics” means each sale contributes little — or worse, the variable cost exceeds the price, so every sale loses money and selling more just digs the hole deeper.

Remember: a positive contribution margin is the price of admission. If Foundry lost money on every part, no amount of scale would save it — you can’t make it up in volume. Growth only helps once each unit already contributes something.

Why investors obsess over it

This is the lens behind a lot of “efficiency era” scrutiny. A company can post huge revenue and still be a bad business if each sale barely contributes — because its fixed costs and marketing swallow everything. Foundry’s healthy $40-per-part contribution is the signal that more volume produces more profit rather than bigger losses. It’s also why two companies with the same revenue can be valued completely differently.

Fixed or variable?

Drag each Foundry cost into the right bucket — or tap an item, then a bucket.

Spot the healthy unit

Tap each card to see whether the unit economics work.

How to use it

Next time someone celebrates fast growth, ask the unit-economics question: “What’s the contribution margin per sale, and how many do we need to break even?” It cuts straight through vanity. For Foundry, each part contributes $40 and break-even is 75,000 parts against 100,000 sold — so more volume genuinely means more profit. If each unit barely contributes — or loses money — then “let’s scale” is a plan to lose money faster. Useful phrases: “Is that cost fixed or variable?” “What does one more part actually net us?” “Where’s break-even?” Those questions mark you as someone who reads past the top line.