Inventory basics for a small online store: SKUs, stock counts and reorder points

Inventory is the sellable stock sitting on your shelves right now. If you track it poorly, you will either sell items you do not own—upsetting customers and causing cancellations—or tie up scarce startup cash in dead stock sitting in cardboard boxes.

Getting inventory right on your first store does not require complex warehouse enterprise software. It takes five simple habits: giving each product variant a clear SKU code, turning on inventory tracking in your store admin, deciding what happens at zero stock, calculating a reorder point, and doing regular physical counts.

Worked example: reorder points and the carrying cost of holding stock

Managing physical stock balances two risks: order too little and you run out of stock; order too much and cash sits trapped in unsold boxes.

Here is a realistic worked example showing how reorder math and stock holding work. Both stores sell a hypothetical product at a $40 retail price, with a product cost of $14 per unit from a supplier.

Store A: steady local supplier

Store A sells 4 units a day (120 units a month). The local supplier delivers orders in 7 calendar days. The owner keeps a 5-day safety buffer (20 units) for delivery delays or sales spikes.

• Daily sales: 4 units
• Supplier lead time: 7 days
• Safety stock buffer: 4 units/day × 5 days = 20 units
• Lead time demand: 4 units/day × 7 days = 28 units
• Reorder point: 28 units + 20 units = 48 units

When inventory drops to 48 units, Store A reorders. During the 7 days while the batch ships, Store A sells 28 units, leaving exactly the 20-unit buffer when stock arrives.

Store B: long-lead supplier

Store B sells the same 4 units a day (120 units a month), but orders from an overseas supplier that takes 30 days to deliver, with a 10-day safety buffer (40 units).

• Lead time demand: 4 units/day × 30 days = 120 units
• Safety stock buffer: 4 units/day × 10 days = 40 units
• Reorder point: 120 units + 40 units = 160 units

The cash impact

At a wholesale cost of $14 per unit:

Store B must keep $1,568.00 more cash tied up on shelves ($2,240.00 − $672.00 = $1,568.00) simply because of supplier lead time. Every extra week your supplier takes forces more cash into safety stock.

Run it with your own numbers: Reorder point = (average daily unit sales × supplier lead time in days) + safety stock units. Check your net profit on each unit before ordering stock with our profit per order calculator.

How to set up SKUs that keep your catalog organized

A SKU (stock keeping unit) is an internal code you assign to track inventory and report on sales. SKUs are internal codes tailored to your store, distinct from universal manufacturer barcodes.

Platforms like Shopify do not require a SKU to publish an item, but using them pays off immediately:

• Accurate tracking: Search stock lists instantly by code.
• Clean reports: Sales break down cleanly by variant.
• Fewer packing errors: Packers pick the exact code on the packing slip.
• Third-party syncing: Shipping tools like ShipStation and outside apps need unique SKUs to sync inventory.

One SKU per variant

Every variant needs its own SKU. A shirt in 3 sizes and 4 colors has 12 variants and needs 12 distinct SKUs. If two variants share a SKU, stock counts blur together.

For example, a walnut pen with black ink and a 2.5 mm point uses WAL_BLK_25. If you later use Shopify Fulfillment Network, unique SKUs for each variant are required.

Tracking inventory in your ecommerce platform

Your online store platform provides the central database for all stock counts.

Shopify inventory setup

• Enable tracking: Check “Track quantity” under the Inventory section for each variant.
• View inventory history: Shopify stores an adjustment history for up to 180 days to trace sales, corrections, and app changes.
• Stock adjustments: View levels, adjust quantities, and manage stock counts in your admin.
• Stock alerts: Shopify does not send low-stock emails out of the box. Use Shopify Flow or an inventory alert app from the Shopify App Store.
• Inventory apps: If an app tracks a product’s inventory, Shopify allocates those quantities only to that app’s location.

WooCommerce inventory setup

• Variation stock: Each variation of a variable product can have its own price, SKU, and stock level.
• Bulk editing: Bulk edit tools let you adjust stock counts or prices for many products at once.
• Stock notifications: Threshold settings for low-stock and out-of-stock alerts live under WooCommerce > Settings > Products.

Decide what happens at zero stock

When an item hits zero stock, Shopify offers the continue selling when out of stock setting.

Leave out-of-stock selling off (the default)

For most stores, leave it turned off. When stock hits zero, your store displays Sold Out and stops checkout.

Selling items you do not have risks late shipping penalties. Under the FTC’s Mail, Internet, or Telephone Order Merchandise Rule, sellers must have a reasonable basis for stated shipping times (or ship within 30 days if no time is stated). If a delay occurs, you must notify the buyer, state a revised date, and offer cancellation with a prompt refund (within 7 working days, or one billing cycle for credit cards).

Only turn out-of-stock selling on for formal pre-orders with clear ship dates, or fast supplier restocks within 24 to 48 hours.

Two critical traps

• Shopify POS: The continue selling when out of stock setting does not apply to Shopify POS. Staff can keep selling through zero stock; POS displays a warning before checkout but does not block the sale.
• Shopify Payments refund fees: If you oversell and issue a refund, Shopify Payments does not refund credit card fees (2.9% + 30¢ on Shopify Basic). On a $40 order, that is $1.46 lost. Learn more in our returns and refunds process guide.

When you do not need to hold inventory

If holding stock sounds daunting, alternative models let you sell with zero inventory carrying cost:

Print on demand (POD)

Print on demand lets you sell custom goods produced after the order arrives:

• Printful: Produces every item to order with zero unsold inventory. The Free plan is $0/month; Growth is $24.99/month (free at $12,000/year in sales).
• Printify: No inventory and no warehouses. Free plan is $0/month; Premium starts at $24.99/month on annual billing ($39/month monthly).

Compare models in Printful vs Printify and print on demand explained.

Dropshipping

Shopify notes dropshipping lets you sell without handling inventory or shipping. A supplier ships directly to the customer. You stay responsible for customer service and order tracking. See dropshipping explained.

Common inventory mistakes

1. Skipping SKUs early. Creating SKUs after launching dozens of products is a painful relabeling chore. Set the format before launch.
2. Guessing reorder timing. Ordering only when shelves look empty guarantees you run out while waiting on supplier lead times.
3. Ignoring physical counts. Software stock counts drift from damaged goods and returns. Count stock regularly to keep records accurate.
4. Tying up cash in bulk discounts. Buying 500 units for a 10% discount traps working capital in unproven items. Buy small batches first.
5. Forgetting return restocks. When a return arrives in good condition, restock it in your admin so you do not lose track of sellable stock.

What to do this week: a 5-step checklist

1. Draft your SKU syntax: Choose a clean alphanumeric format (like CAT-PROD-VAR) and record your abbreviation rules.
2. Assign SKUs to every variant: Add unique SKUs across Shopify or WooCommerce.
3. Turn on tracking and enter verified counts: Enable “Track quantity” and enter real shelf counts.
4. Leave out-of-stock selling off: Keep “Continue selling when out of stock” disabled unless running clear pre-orders.
5. Set reorder points for top items: Use (Daily sales × Lead time) + Safety buffer and schedule calendar reminders.

For monthly budget planning, see our guide to the monthly cost of running an online store and our launch checklist.

This guide provides operational information, not legal or tax advice.

Sources (checked 2026-10-03)

• Shopify Help Center: Using SKUs to manage your inventory, SKU purpose, rules, uniqueness, and Shopify Fulfillment Network requirements
• Shopify Help Center: Managing inventory, inventory overview, tracking setup, low-stock alert apps, and Shopify Flow
• Shopify Help Center: Setting up inventory tracking, 180-day history, out-of-stock selling settings, POS behavior, and app locations
• Shopify Help Center: Setting up your product inventory, inventory levels and fulfillment process relationships
• Shopify Help Center: Refunding orders, restock options and non-refundable credit card fees on Shopify Payments
• Shopify Pricing, Shopify plan rates, card fees, and monthly pricing
• WooCommerce: Adding and managing products, variable product SKUs, stock levels, and bulk editing
• WooCommerce: Configuring WooCommerce settings, inventory management and low-stock notification settings
• FTC: Mail, Internet, or Telephone Order Merchandise Rule, reasonable basis for shipment representations, delay notice requirements, and refund deadlines
• Shopify Help Center: Dropshipping, dropshipping fulfillment model and merchant responsibilities
• Printful: Pricing, made-to-order fulfillment, zero unsold inventory, Free and Growth plan pricing
• Printify: Pricing, zero inventory model, Free and Premium plan pricing
• ShipStation Pricing, carrier discounts and ecommerce integrations