What Are Unit Economics?
Unit economics refers to the direct revenues and costs associated with a single unit of business activity — in e-commerce, typically one order or one product sold. They answer the question: is each individual transaction fundamentally profitable, before considering fixed overheads?
Unit economics sit at the heart of every sound e-commerce business model. They're the reason two businesses with identical revenue can have completely different trajectories: one with strong unit economics grows profitably; one with weak unit economics grows into bigger losses.
The Scaling Principle
If your unit economics don't work at 50 orders a day, they won't work at 500. Scale amplifies both the strengths and weaknesses of your unit-level model. Fix the unit economics first — then scale confidently.
Key Unit Economics Metrics
| Metric | Definition | How to Calculate |
|---|---|---|
| Revenue per unit | Average selling price net of discounts and promotions | Total net revenue ÷ units sold |
| COGS per unit | Direct product cost including landed costs, duties | Total COGS ÷ units sold (or per SKU) |
| Gross margin per unit | Revenue minus COGS per unit | Revenue per unit − COGS per unit |
| Fulfillment cost per unit | Pick, pack, ship, packaging, and handling per order | Total fulfillment cost ÷ orders |
| Payment processing per unit | Card and platform fees per transaction | ~2.9% + £0.30 (Stripe) or equivalent |
| Return cost per unit | Blended return cost allocated to all units sold | (Return rate × cost per return) ÷ total units |
| Contribution margin per unit | Revenue minus all variable costs per unit | Sum of all above reductions from revenue |
| CAC per unit | Customer acquisition cost allocated to each sale | Total ad + marketing spend ÷ total orders |
| Net profit per unit | Contribution margin minus allocated fixed costs and CAC | CM per unit − (fixed costs/unit) − CAC |
Building Your Unit Economics Model
A complete unit economics model builds from revenue down to net profit per unit, layer by layer:
WORKED EXAMPLE: Sportswear Brand
Average selling price: £95
- Less COGS (branded sportswear): −£38.00
- Less fulfillment (pick, pack, ship): −£7.50
- Less packaging: −£1.20
- Less payment processing (2.9% + £0.30): −£3.06
- Less return allowance (15% return rate × £13 cost): −£1.95
Contribution margin per unit: £43.29 (45.6%)
- Less allocated fixed costs (warehouse, team, software ÷ units): −£12.00
- Less ad spend per sale (blended CAC): −£22.00
Net profit per unit: £9.29 (9.8%)
This brand is operating at 9.8% net margin per unit sold. If the CAC rises above £31.29, the unit becomes loss-making after fixed cost allocation.
How Unit Economics Break Down at Scale
Unit economics are not static — they evolve as your business grows, sometimes in your favour and sometimes against you.
Ways Unit Economics Improve at Scale
- Supplier pricing: Volume discounts reduce COGS per unit
- Carrier rates: Higher parcel volume unlocks better shipping rates
- Fixed cost dilution: Warehouse and team costs spread across more units
- Brand awareness: Organic traffic reduces reliance on paid acquisition, lowering effective CAC
Ways Unit Economics Deteriorate at Scale
- Rising CAC: The most efficient customer segments are acquired first. As you grow, you must target harder-to-reach customers at higher cost.
- Operational complexity: More SKUs, more returns, more customer service complexity can raise per-unit costs
- Margin compression: Growth often attracts competitors, putting downward pressure on prices
- Return rate creep: As you broaden your customer base, you may see higher return rates from new customer segments
Monitor CAC Trends Monthly
Rising CAC is the earliest warning sign that unit economics are deteriorating. If CAC grows faster than LTV, your growth is becoming progressively less profitable. Catch this in month 3 or 4 — not after 12 months of compounding loss.
Using Unit Economics to Evaluate New Products
Before investing in new product inventory, run a unit economics model. This is especially important for new SKUs in categories you haven't sold before.
New Product Pre-Launch Unit Economics Template
Assumptions to estimate:
- Expected selling price (based on competitor research)
- COGS (supplier quote + landed costs)
- Fulfillment (use your existing per-order costs)
- Expected return rate (use category benchmark if unknown)
- Target CAC (use your existing blended CAC as baseline)
Decision rules:
- Contribution margin below 25%: only advertise if CAC can be very low
- Contribution margin 25–40%: viable for advertising at efficient CAC
- Contribution margin above 40%: prioritise for advertising — this is a margin star
This pre-launch modelling takes 30 minutes and can save you from investing in inventory for products that cannot generate acceptable returns from advertising.
Unit Economics and Google Shopping Profitability
Every Google Shopping sale is a unit economics event. The ad spend that generated the sale is a direct cost that must fit within the contribution margin of the unit sold.
The relationship is direct:
- If contribution margin per unit = £40 and your ad spend per sale is £25, you have £15 remaining for fixed costs and profit. Good.
- If contribution margin per unit = £40 and your ad spend per sale is £45, you are losing £5 per sale on advertising before even counting fixed costs. Unsustainable.
This is why ROAS targets must be derived from unit economics — not set based on industry benchmarks or historical habit. The correct maximum ad spend per unit is a function of your specific product's contribution margin and your profit target.
| Contribution Margin | Max Ad Spend (Zero Profit) | Max Ad Spend (15% Net Profit Target) |
|---|---|---|
| £20 (20% on £100 product) | £20 | £5 |
| £35 (35% on £100 product) | £35 | £20 |
| £50 (50% on £100 product) | £50 | £35 |
| £80 (40% on £200 product) | £80 | £50 |
The table illustrates why low-margin products are so difficult to advertise profitably — and why product mix matters so much in Google Shopping strategy.
Frequently Asked Questions
What are unit economics?
Unit economics refers to the revenue, costs, and profit associated with a single unit of sale. For e-commerce, a "unit" is typically one order or one product sold. Understanding unit economics tells you whether your business model is fundamentally profitable.
What are the key unit economics metrics for e-commerce?
Revenue per unit, COGS per unit, gross margin per unit, fulfillment cost per unit, payment processing cost per unit, return cost per unit, and CAC per unit (customer acquisition cost allocated to each sale).
How do unit economics break down at scale?
Unit economics can deteriorate at scale if variable costs increase (e.g. hiring more staff to fulfill orders raises per-unit labor costs) or if marketing efficiency declines (you exhaust the cheapest customer acquisition channels and CAC rises). Watch both metrics as you scale.
Can I use unit economics to evaluate new product launches?
Yes — unit economics modelling lets you estimate profitability before committing to stock. By estimating selling price, COGS, fulfillment, and expected return rate, you can calculate whether a new product is worth listing and advertising before investing in inventory.
How do unit economics relate to Google Shopping profitability?
Each Google Shopping sale should generate positive unit economics after all costs including ad spend. If your unit economics show £40 contribution margin on a product, your maximum ad spend per sale is £40. Exceeding this makes the unit unprofitable regardless of ROAS.
Next Steps
Sound unit economics are the foundation of profitable growth. Once you know the true economics of each unit you sell, you can make rational decisions about which products to advertise, how much to bid, and when to scale.
Build Per-Unit Cost Visibility with GROW
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