Inventory Turnover Ratio: How to Calculate and Improve It (UK Guide)

The formula

Inventory turnover = Cost of Goods Sold ÷ Average inventory value

Both numbers are at cost, not retail price. Cost of Goods Sold (COGS) is what you paid for the stock you sold during the period. Average inventory smooths out the peaks and troughs of restocking — the simplest version is:

Average inventory = (Opening stock value + Closing stock value) ÷ 2

If your stock levels swing a lot (seasonal buying, big container orders), averaging month-end values across the year gives a much truer picture than just opening and closing.

Worked example

A seller's COGS for the year is £84,000. Stock was worth £16,000 at the start of the year and £12,000 at the end:

• Average inventory = (£16,000 + £12,000) ÷ 2 = £14,000
• Turnover = £84,000 ÷ £14,000 = 6.0

This business sells through its typical stock holding six times a year. Every pound invested in stock comes back — with margin on top — roughly every two months.

A common mistake: using revenue instead of COGS

Some guides divide revenueby inventory value. That mixes retail prices (numerator) with cost prices (denominator), inflating the ratio by your margin. It isn't useless — it's consistent over time for the same business — but it makes category benchmarks meaningless and flatters high-margin sellers. Use COGS.

Days of inventory: the same number, made intuitive

Days Sales of Inventory (DSI) = 365 ÷ turnover ratio.

A turnover of 6 is 61 days of inventory. A turnover of 2 is 183 days — half a year between paying your supplier and getting the money back. DSI is often the more useful framing because it maps directly onto cash flow: if your supplier wants payment in 30 days but your stock takes 90 days to sell, you are financing 60 days of stock from your own pocket, forever.

What's a good ratio?

Category dominates everything here. Rough working ranges for small UK ecommerce sellers:

Treat these as orientation, not targets — margins matter as much as speed. A jeweller turning stock 2.5 times a year at 60% margin is a healthier business than a consumables seller turning 10 times at 12%. The most useful comparison is your own trend: is this quarter's ratio better or worse than the last four?

Can turnover be too high?

Yes — and this is the trap in treating turnover as a score to maximise. A climbing ratio is only good news if your availability holds. If you are hitting stockouts, your turnover is high because you are under-buying, and every stockout costs you:

• Direct sales during the gap,
• Marketplace ranking — eBay and Amazon both demote listings that go out of stock, and recovery takes weeks, and
• Repeat customers, who buy from whoever had it in stock.

Watch turnover and stockout rate together. The goal is the highest turnover you can sustain at near-100% availability on your A items — which is why turnover pairs naturally with ABC analysis.

Seven ways to improve your turnover

1. Find where the cash is stuck — per SKU

A whole-business ratio hides everything interesting. Calculate turnover (or simply days of cover: current stock ÷ average daily sales) per SKU, and sort. Almost always you will find a handful of products holding six-plus months of stock. That is your dead and excess stock — deal with those first and the business-level ratio moves on its own. Our dead stock guide covers the clearing playbook.

2. Buy less, more often

The single biggest lever. If you order 6 months of stock at once, your average inventory is ~3 months of sales; order 2 months at a time and it drops to ~1 month — turnover triples with identical sales. The trade-offs are real (unit price breaks, shipping cost per order, supplier minimums) — the EOQ framework is the structured way to find the balance.

3. Set reorder points instead of gut-feel ordering

Gut-feel ordering over-buys slow movers (they feel risky) and under-buys fast movers (they feel fine until they aren't). A calculated reorder point per SKU replaces both errors with a rule.

4. Sell everywhere your stock can sell

The same stock listed on one channel turns slower than the same stock listed on four. Multi-channel listing is a turnover strategy: each additional marketplace is extra demand against the same inventory investment. The catch is keeping quantities in sync — which is a solved problem with the right tooling.

5. Cut the tail

Fewer, better SKUs turn faster. Every quarterly review, ask of each C-class product: would I buy this again today? Discontinuing the bottom 10% of your catalogue typically costs ~1–2% of revenue and frees a disproportionate share of cash and space.

6. Use pre-orders and dropship for slow high-ticket items

If a £400 item sells four times a year, holding it in stock gives you a turnover of 1–2 on that SKU. Taking it on pre-order or dropshipping itgives you infinite turnover on capital you never deploy. Keep stock for what turns; broker what doesn't.

7. Fix your data before optimising anything

Turnover calculated from wrong stock values is noise. If your recorded quantities drift from reality, start with counting discipline and accurate cost prices. Only then do the ratios mean anything.

Tracking it without spreadsheets

The calculation needs your COGS and stock value over time — data that lives in your inventory system, not your memory. Salync's reports track inventory valuation continuously and show sales velocity and days-of-cover per SKU across all your channels, so slow stock surfaces before it becomes dead stock. You can try it on the free plan with up to 50 SKUs.