How much to reorder on Shopify: the quantity math
Checked against the live sources below on 27 October 2026.
Order enough to cover sales until the next delivery arrives, plus safety stock, minus what you already have and what is already on order. In one line: daily sales × days to cover + safety stock − on hand − on order. The reorder point calculator gives the level that should trigger the order.
The formula in plain steps
- Decide how many days one order should last, for example 45.
- Multiply by average daily sales.
- Add safety stock for supplier delays and demand spikes.
- Subtract units on hand and units already ordered.
- Round up to your supplier’s minimum or case size.
Do this per product, not for the whole store: a fast seller and a slow seller need different cover, and one blended number is wrong for both.
A worked example with invented numbers
A product sells 12 a day. You want 45 days of cover: 540 units. Safety stock is 60. You have 200 on hand and 100 on order. Order 540 + 60 − 200 − 100 = 300 units. If the supplier sells in cases of 24, round up to 312.
When order cost and holding cost matter
The classic economic order quantity model picks the order size that minimises ordering costs plus holding costs. Wikipedia notes it assumes constant demand and that each order arrives in full when inventory reaches zero, so treat it as a starting point rather than an answer. If each order costs you a lot to place or ship, order bigger and less often; if storage or cash is tight, order smaller and more often.
Practical limits
- Minimum order quantities can force you above the formula.
- Cash. Cover days you can afford, not days you want.
- Shelf life and trends. Cut cover for items that expire or fade.
- Review rhythm. Recheck fast sellers every cycle and slow sellers monthly, since the inputs change.
Shopify’s help center says you can create purchase orders from your Shopify admin, so the number you work out can become the order. Restockly’s vendor-grouped reorder list, per its listing, lets you edit suggested quantities before you copy them out.
Find the stock level that should trigger your next order.
Reorder point calculator Restockly for ShopifyFrequently asked questions
How many days of stock should I order?
It depends on your cash, your supplier’s minimums and how fast the product sells. There is no single right answer, so test a number and review it each cycle.
What if my supplier has a minimum order?
Order at least the minimum, and consider whether the extra stock is worth its holding cost. If it is not, ask about smaller runs.
Does Restockly calculate quantities?
Its listing says it suggests reorder quantities you can edit before copying the list into an email or spreadsheet.
How this page was researched
Read on 27 October 2026. The arithmetic is standard and the numbers are invented; the order-quantity model comes from Wikipedia; Shopify purchase orders come from its help center; Restockly’s list comes from its live listing.
- Wikipedia: Economic order quantity — EOQ is the order quantity that minimises total holding and ordering costs; it assumes constant demand and each order delivered in full when inventory reaches zero
- Wikipedia: Safety stock — the reorder point is the inventory level that triggers an order; lead time is the delay before renewed availability; a higher service level needs more safety stock
- Shopify Help Center: Inventory and locations — purchase orders can be created from your Shopify admin; each links to an inventory transfer that tracks the shipment
- Restockly on the Shopify App Store — free; reads your sales history and current stock; four tiles (Order now, Order soon, Stocked, No sales); a live 60-day sales scan with days-of-stock and a reorder-by date on every row; a vendor-grouped reorder list with editable suggested quantities you can copy into an email or spreadsheet
Related: Reorder point calculator · Inventory forecasting basics · Restockly