Direct answer: Launch stock ≈ Expected sessions × Conversion rate × Units per order × Weeks of coverage. Add a safety buffer, and confirm your reorder-by date falls before you sell out.
This guide walks Shopify sellers through the launch inventory math and links to a free browser calculator.
Who this is for
Shopify DTC brands launching a new product or SKU line who want to size the first purchase order without over- or under-stocking.
Inputs you need
- Expected launch-week sessions from email, paid, and organic.
- Realistic conversion rate (start with 1.5–2.5% for new SKUs).
- Units per order.
- Weeks of coverage before the reorder should arrive.
- Supplier lead time.
- Safety-stock buffer.
- Landed cost per unit.
The formula
Launch units = Sessions × Conversion rate × Units per order × Coverage weeks.
Reorder-by day = Launch day + (Coverage weeks × 7) − Lead time.
Illustrative launch scenarios
| Scenario | Sessions/wk | CVR | Coverage | Launch units |
|---|---|---|---|---|
| Cautious | 4,500 | 2.0% | 4 wks | ~430 |
| Base | 4,500 | 2.2% | 6 wks | ~715 |
| Aggressive | 6,000 | 2.5% | 8 wks | ~1,440 |
Example calculation (USD)
A skincare brand expects 4,500 launch-week sessions, 2.2% CVR, 1.2 units per order, and wants 6 weeks of coverage. Weekly units = 4,500 × 0.022 × 1.2 ≈ 119. Launch stock = 119 × 6 = 713. Adding a 20% safety buffer = 856 units. If landed cost is $9, capital required ≈ $7,700. Lead time is 28 days, so reorder-by day = 42 − 28 = day 14 after launch.
Common mistakes to avoid
- Assuming steady-state conversion rate for a brand-new SKU.
- Not splitting launch stock into a smaller first shipment + air-freight top-up when capital is tight.
- Ignoring returns — 10% of stock never comes back to sellable.
- Skipping a Plan B for slower-than-expected launch.
Best practices
- Model three scenarios (cautious, base, aggressive) and pick the middle.
- Ask the supplier for a partial-quantity re-order to reduce lead-time risk.
- Set a hard reorder trigger in your inventory sheet by day 14.
Frequently asked questions
How do I estimate launch traffic?
Email list × open rate × click rate + paid session forecast, discounted 20–30% for reality.
Is it better to under- or over-stock a launch?
For unproven SKUs, slightly under-stock and airship a top-up. For proven brands, stock deeper.