Retail replenishment is one loop: know when each SKU needs reordering, decide how much against pack sizes and minimums, send each supplier their order, receive what actually arrives at what it actually cost, and let the result sharpen the next reorder. Run it well and cash sits in the right inventory; run it from memory and you stock out of winners while dead stock eats the storeroom.
This is the hub for the whole loop for retailers — Shopify and brick-and-mortar POS alike. Each section gives the working version, then links the deep guide, tool, and concept pages. It's the retail sibling of Restaurant Purchasing, Complete.
Step 1: Know when to reorder — computed, not vibes
The core object is the reorder point: expected demand during the supplier's lead time, plus safety stock sized to demand and lead-time variability. Every POS offers some version of a low-stock threshold; none of them compute it for you, and a hand-set threshold that was right in March is wrong in November — which is why best-sellers still stock out.
- Compute it: Reorder Point Calculator · Par Level Calculator
- Classify first: Demand Pattern Classifier — smooth, intermittent, erratic, and lumpy SKUs need different math
- Per-POS reality: Shopify low stock alerts · Lightspeed reorder report
Step 2: Decide how much — quantity is a different question than when
Order quantity balances pack sizes, supplier minimums, price breaks, carrying cost, and how much capital you want sleeping on shelves. The formal tools: economic order quantity, minimum order quantities, and — for seasonal buying against a budget — open-to-buy.
- Deep guide: Best Inventory Replenishment Software
- Watch the trap: carrying cost — volume discounts that lose money
Step 3: Create and send the purchase orders
One PO per supplier, in the channel that supplier actually works in. The per-POS walkthroughs, source-checked against official docs:
- How to Create Purchase Orders from Shopify — native POs, transfers, and the can't-email-the-supplier gap (and if you're on Stocky: it stops working August 31, 2026)
- Square Inventory Purchase Orders — full setup, and the suspended auto-PO feature
- Lightspeed: reorder report to PO · the procurement layer
- No system at all yet? Purchase Order Generator and how to write a purchase order
Step 4: Track what the supplier says back
The order you sent is not the order you'll receive. Confirmations, shorts, substitutions, price changes, and moved ETAs arrive by email and portal — and in most retail stacks, nothing records them against the PO. This is the gap that turns receiving into archaeology and it's where the living purchase order model earns its name.
- Deep guides: How AI Reads Your Supplier Emails · The 4:47 PM Supplier Reply
Step 5: Receive and reconcile costs
Receiving checks the truck against the confirmed order; costs update from what you actually paid, including freight and duties. The concepts that keep COGS honest: weighted average cost, landed cost, purchase price variance. Note that Shopify's cost-per-item field never updates at receiving, by design.
- Template: Receiving Checklist CSV
- Control model: Three-Way Matching vs Living POs
Step 6: Manage the catalog the loop runs on
Replenishment quality is capped by catalog hygiene: ABC analysis to focus effort, SKU rationalization to cut the long tail, GMROI and inventory turnover to judge what deserves shelf space, cycle counts to keep the on-hand numbers real.
Scaling past one location
Central warehouse feeding branches, transfer-vs-purchase decisions, and per-location replenishment with consolidated buying:
- Central Warehouse Procurement for Multi-Location Retail
- Procurement for Retailers — and the vertical pages for convenience stores, wine shops, pet stores, and cannabis retail
Running the whole loop in one system
Every step has a manual version, and steps 1–2 have free calculators above. The compounding upgrade is connecting them: sales velocity drives computed reorder points per SKU, suggested orders respect packs and minimums and inbound POs, orders go out per supplier in their channel, replies update the living PO, receiving reconciles against the confirmed state, and clean costs land in accounting. That's closed-loop procurement, and running it beside your POS — Shopify, Square, Lightspeed, or Clover stays exactly where it is — is what LineNow does, with a 90-day free trial long enough to run real supplier cycles.
Start where it hurts: stockouts on best-sellers → step 1; cash tied up in slow stock → steps 2 and 6; surprises at the receiving door → steps 4 and 5.