How to Calculate Sell Rate for Shopify Products

Sell rate (also called sales velocity or sell-through rate) tells you how quickly a product moves through your inventory in a given period. To calculate it: divide units sold by the number of days in the period. For example, selling 90 units over 30 days gives you a sell rate of 3 units/day. That single number drives every smart reorder decision you'll make.

If you're running a Shopify store, sell rate is the foundation of inventory management. Get it right and you'll stop scrambling to reorder before you hit zero. Get it wrong — or ignore it entirely — and you're either sitting on dead stock or losing sales because a best-seller went out of stock on a Tuesday afternoon.

---

What Is Sell Rate (and How Is It Different from Sell-Through Rate)?

These two terms get used interchangeably, but they measure slightly different things.

Sell rate (or sales velocity) measures how many units you sell per unit of time — typically per day or per week. It's a forward-looking number you use to forecast how long your current stock will last.

Sell-through rate measures what percentage of your available inventory you've sold within a specific period. It's expressed as a percentage, and it's more useful for evaluating how a product performed relative to what you stocked.

Metric	Formula	Output	Best Used For
Sell Rate	Units Sold ÷ Days in Period	Units/day	Forecasting, reorder timing
Sell-Through Rate	(Units Sold ÷ Units Received) × 100	Percentage	Performance evaluation, buying decisions

Both matter. But if your primary goal is answering "when do I need to reorder this product?", sell rate is the number you want.

---

The Sell Rate Formula

Sell Rate = Units Sold ÷ Number of Days in Period

That's it. No complicated math. The challenge isn't the formula — it's choosing the right time period and knowing what to do with the result.

Example: You sell a candle that moved 120 units over the past 60 days.

120 ÷ 60 = 2 units/day

Your sell rate is 2 units/day. If you have 50 units left in stock, you have roughly 25 days of inventory remaining.

---

Step-by-Step: How to Calculate Sell Rate in Shopify

Here's a practical walkthrough using data you can pull directly from your Shopify admin.

Step 1: Pull your sales data

Go to Shopify Admin → Analytics → Reports → Sales by product. Set the date range to the last 30, 60, or 90 days. Export or note down units sold per SKU.

Step 2: Choose your time window

This matters more than most guides admit. A 7-day window is too noisy — one viral TikTok or a flash sale skews everything. A 90-day window smooths out volatility but can miss recent trend shifts. For most DTC Shopify stores, 30 days is a solid default, with 60-90 days used for slower-moving products.

Step 3: Apply the formula

Sell Rate = Units Sold in Period ÷ Number of Days in Period

For a product that sold 45 units in 30 days:

45 ÷ 30 = 1.5 units/day

Step 4: Calculate days of stock remaining

Days of Stock = Current Inventory ÷ Sell Rate

If you have 90 units on hand:

90 ÷ 1.5 = 60 days of stock

Step 5: Calculate your reorder point

Reorder Point = Sell Rate × Lead Time (in days) + Safety Stock

If your supplier takes 14 days to deliver and you want 7 days of safety stock:

1.5 × 14 + (1.5 × 7) = 21 + 10.5 = 31.5 → reorder when you hit 32 units

---

Which Time Period Should You Use?

The time window you choose for sell rate calculations has a bigger impact on accuracy than most store owners realize. Here's a practical guide:

Last 7 days — Only useful for fast-moving products during a known stable period. Easily distorted by weekends, promotions, or a single large order.

Last 30 days — The default for most Shopify merchants. Balances recency with enough data to be statistically meaningful. Good for products selling 10+ units/month.

Last 60–90 days — Better for slower SKUs (1–5 units/month). Gives you enough sample size to avoid making decisions based on noise.

Seasonality adjustment — If you're selling sunscreen in March, your last 30-day sell rate from November is useless for summer planning. Use the same period from last year as a baseline, then adjust for growth.

A useful rule of thumb: use a time window that contains at least 20–30 sales events for the SKU. If a product only sells 3 times a month, use 90 days of data.

---

Sell Rate vs. Sell-Through Rate: When to Use Each

Use sell rate when you're asking:

• How long will my current stock last?
• When should I reorder?
• How many units should I order?

Use sell-through rate when you're asking:

• Was this product a success relative to what I bought?
• Should I discount this SKU to clear it out?
• Did this season's buy make sense?

For most operational inventory decisions — the day-to-day "do I need to reorder yet?" questions — sell rate is your go-to metric. Sell-through rate is more of a post-mortem tool.

What's a good sell-through rate? Most retail benchmarks suggest 80% or higher within the intended selling window is healthy. Below 60% often signals overbuying, weak demand, or pricing issues. Above 90% consistently might mean you're underbuying and leaving sales on the table.

---

Common Mistakes When Calculating Sell Rate

Using total inventory received instead of units sold Some merchants accidentally flip the formula and calculate what percentage of stock remains rather than how fast it's moving. Double-check: sell rate is units sold over time, not units remaining.

Ignoring stockout periods If a product was out of stock for 10 days during your 30-day window, your sell rate will be artificially low. Those 10 days of zero sales skew your average downward. When a SKU had stockout days, either exclude that window from your calculation or adjust for it: use units sold ÷ (days in stock, not total days).

Using the same time window for every SKU A flagship product selling 50 units/day and a niche variant selling 2 units/month need different calculation windows. One formula fits all is a shortcut that costs you accuracy.

Not accounting for trend Sell rate assumes the future looks like the past. If a product is trending up (new press mention, seasonal ramp-up), a flat historical average will underestimate demand. Layer in a growth factor when you have evidence of acceleration.

---

How to Use Sell Rate to Set Reorder Points

Sell rate on its own is just a number. It becomes actionable when you connect it to your reorder point — the inventory level at which you trigger a purchase order.

The full reorder point formula:

Reorder Point = (Sell Rate × Lead Time) + Safety Stock

Where:

• Sell Rate = units/day (your calculated average)
• Lead Time = days from placing an order to receiving stock
• Safety Stock = buffer inventory to cover demand spikes or supplier delays

Worked example:

A skincare store sells a moisturizer at 4 units/day. Their supplier in South Korea has a 21-day lead time. They want 10 days of safety stock.

Reorder Point = (4 × 21) + (4 × 10) = 84 + 40 = 124 units

When inventory hits 124 units, it's time to place an order — not when you're scrambling at 10 units left.

This is exactly the kind of calculation that Alertr automates. Rather than running these numbers manually in a spreadsheet every week, Alertr tracks sell rate per SKU across your Shopify catalog and fires an alert — via email or Slack — when a product crosses its reorder threshold. For stores managing 50–500 SKUs, that automation prevents the "oh no, we're out of stock" moment that usually happens at 11pm on a Friday.

---

Sell Rate by Product Category: What to Expect

Not all sell rates are created equal. Here's a rough benchmark by category for Shopify DTC brands:

Category	Typical Daily Sell Rate	Reorder Frequency
Consumables (supplements, skincare)	High (5–50+/day)	Weekly to monthly
Apparel (core styles)	Medium (1–10/day)	Monthly
Apparel (seasonal/limited)	Variable	Per season
Home goods	Low (0.1–2/day)	Quarterly
Accessories	Low-medium (0.5–5/day)	Monthly to quarterly

If your sell rate is well outside these ranges, it's worth investigating — either you've got a breakout product that needs more aggressive inventory planning, or you've got a slow mover tying up cash.

---

Automating Sell Rate Tracking for Shopify

Manually pulling 30-day sales data for every SKU, running the formulas, and checking reorder points is fine when you have 10 products. At 100+ SKUs, it becomes a part-time job — and it's one of those jobs that tends to get skipped right before a stockout hits.

The most practical approach:

1. Start with spreadsheets if you have fewer than 30 SKUs. Build a simple template with columns for units sold (30-day), sell rate, current stock, days remaining, and reorder point.

2. Move to an app once you're managing 50+ SKUs or spending more than 30 minutes/week on this manually. Tools like Alertr, Stockie, or Prediko pull this data automatically from Shopify and surface it when action is needed.

3. Set alerts, not dashboards. A dashboard you have to remember to check is just a fancier spreadsheet. The real value is in proactive notifications — getting a Slack message when Product X drops below reorder point, rather than logging into a tool and hoping you noticed.

The apps vary significantly in price and complexity: Bee Low Stock Alert runs $5.99/mo and covers the basics; Prediko starts at $49/mo with AI forecasting and purchase order management. Alertr sits in between with a free tier for up to 50 SKUs and a Pro plan at $19/mo (currently locked at beta pricing), with sell rate tracking, configurable thresholds, and Slack/email alerts built in.

---

Quick Reference: Sell Rate Formulas

Sell Rate (units/day)      = Units Sold ÷ Days in Period
Days of Stock Remaining    = Current Inventory ÷ Sell Rate
Reorder Point              = (Sell Rate × Lead Time) + Safety Stock
Sell-Through Rate          = (Units Sold ÷ Units Received) × 100

---

Sell rate is one of those metrics that looks simple on the surface but does a lot of heavy lifting once you start applying it consistently across your catalog. Get in the habit of calculating it regularly — or better yet, let a tool do it automatically — and you'll make fewer reactive inventory decisions and more proactive ones.

If you want Alertr to track sell rate and send you low stock alerts before you need them, start free at getalertr.com. The free tier covers up to 50 SKUs with no credit card required.