Assortment planning for small retailers: width vs depth and the range review
Assortment planning for small retailers: width vs depth decisions, a fill-in range review worksheet, and the gates for adding a new category.
InventoryX is in development and not available today. ClearStock is the live Shopify app.
Assortment planning is deciding what your store sells — how many categories (width), how many products per category (depth), and which specific SKUs make the cut — before any buying happens. For a sub-$2M Shopify store it's the highest-leverage inventory decision there is, because every reorder calculation downstream inherits the range you chose. Buying more of the wrong assortment is efficient execution of a bad decision. This article covers the width-vs-depth tradeoff for small stores, a fill-in worksheet for a quarterly range review, and the gates to clear before adding a category. (Pruning existing SKUs is its own discipline — see the note at the end — and when to place buys is the buying calendar's job; this article owns the composition question.)
Width vs depth: the small-store tradeoff
Width is how many distinct categories or product types you carry. Depth is how many variants, price points, or choices within each. Cash and shelf space force a choice between them, and the tradeoff works differently at small scale than it does for chains:
- Width buys new customers. A new category is a new reason to visit — a spice shop adding board games captures a different trip. But each category carries fixed overhead: supplier minimums, shelf space, the learning curve of its demand patterns.
- Depth buys conversion and loyalty. A deep assortment in one category means the customer who wants the mid-size, mid-price option actually finds it, and comes back before trying another store. Depth concentrates your data too: 60 SKUs of real sales history forecast far better than 300 SKUs of crumbs.
The small-store failure pattern is drift toward width. Every new category starts as "just a few SKUs to test," and the tail compounds: 8 categories × 40 SKUs of thin coverage, none of which is the best in its niche. The alternative failure is over-depth on a niche that's too narrow — 90 SKUs of specialty jerky in a town that wanted 20.
A workable rule from retail practice: be the deepest option available to your customer in every category you keep, or drop the category. A customer comparing you against a specialist will forgive a smaller selection of categories; they won't forgive a worse selection within the one they came for. Treat this as a heuristic, not a law — the point is that mediocrity in the middle of the width-depth dial is the most expensive position.
The range review worksheet (fill it in)
Run this quarterly, category by category. Pull from your Shopify exports: units sold, revenue, and inventory value by SKU for the trailing 90 days (or last season). Then fill in one row per category:
| Input | Where it comes from | What it tells you |
|---|---|---|
| A. Category revenue share | 90-day revenue ÷ total revenue | Whether the category has earned its shelf space at all |
| B. Sell-through spread | Best vs worst sell-through rate within the category | Whether your composition inside the category is right |
| C. Depth utilization | SKUs contributing 80% of category sales ÷ total SKUs | How much of your depth is working (often 20–30%) |
| D. Out-of-stock days | Days key SKUs sat dark during the 90 days | Whether you lost sales to depth buys, not depth choices |
| E. Inventory value | Current category stock at cost | What the category is holding hostage |
Read the five together, with three patterns worth knowing by sight:
- High revenue share + high C + dark D. The category works and your depth is right, but you're under-buying the winners. This is a quantity problem — the range is fine, fix the buys.
- Low A + low C. The category is full of SKUs nobody wanted at this depth. The range itself is wrong — too wide, or the wrong slice of the category.
- High A + terrible B. Your customers want the category but your specific picks miss. Common in stores whose assortment was set by supplier catalogs rather than by sales data — the vendor's bestsellers aren't your customers' preferences.
Worked mini-example: your kitchen section is 22% of revenue (A is healthy), but 8 of 34 SKUs generate 80% of sales (C = 0.24), the worst SKU's sell-through is 6% while the best is 91% (B is terrible), and 14 dark days on the top two SKUs (D). Diagnosis: pattern 3 with a quantity overlay. The answer isn't "add more kitchen SKUs" — it's re-cut the 34 toward the 8 demand clusters, re-derive what the adjacent slots should be from what customers asked for, and buy the winners deeper. Same shelf, same inventory value, tighter range.
When to add a category: the four gates
A new category is a new business line with its own minimums and learning curve. Clear all four gates or wait:
- Gate 1 — Core is deep first. Your main categories show no pattern-2 or pattern-3 problems. Adding width on top of a range that isn't working is avoidance with a purchase order.
- Gate 2 — A tested wedge exists. Not a hunch: pre-orders, a market-stall season, a handful of trial SKUs with real sell-through, or sustained customer requests you can count. The cheapest assortment test is selling a few units before committing to a section.
- Gate 3 — The cash is genuinely free. The trial inventory is funded from profit or a budget line you'd otherwise spend on a deeper buy — not from the reorder money your proven bestsellers need. Cash that skips bestsellers to fund experiments is the most expensive cash in retail, because it's the same dollars your shelf already charges you to hold — the true price of parking it is the inventory carrying cost of the trial stock on top of the opportunity it displaces.
- Gate 4 — You can state the exit. What result in 90 days justifies continuing (e.g., "sell-through above 50% and revenue share above 3%"), and what happens to the stock if it misses. Deciding the kill criteria before buying is what separates a test from an accumulation.
If a category passes all four, start narrow and deep in its hottest sub-niche — not wide and thin. Three suppliers' worth of the one sub-category customers actually asked for beats twelve SKUs scattered across the category. Sizing that first buy is a new-store math problem applied to a section instead of a store: small, aggressive about depth on the obvious winners, and priced to clear.
Composition decisions the data can't make for you
Two assortment calls are judgment, and it's better to make them explicitly than let a spreadsheet imply them:
- The hero-depth halo. Carrying the full depth of a hero category — including the slow, expensive-to-stock end — makes the category credible and lifts the winners. That's a marketing spend expressed as inventory. Make it deliberately, at a size you can afford to underwrite, and review it as a line item rather than letting it grow.
- The deliberate gap. Choosing not to carry the category everyone expects (the nursery without annuals; the bookshop without bestsellers) is a position, not an omission — it frees cash for depth where you win. Own the gap in your merchandising so customers read it as specialization.
Both should appear in your range review notes, so next quarter's you can tell whether the halo earned its keep.
What this article doesn't own
Two adjacent topics have their own homes — use them, don't improvise here:
- Pruning. When the worksheet says your range is too wide, the actual decision framework — the per-SKU test, the exit candidates, what to do with freed cash — is SKU rationalization's territory. The review finds the problem; rationalization owns the cuts.
- Timing. Which months you place buys, how lead times push orders earlier than beginners expect, and the backwards plan from sell-through dates are all covered in the retail buying calendar. Range review decides what exists; the calendar decides when it lands.
One tool note: assortment composition is above what most inventory apps do, including ours. InventoryX (in development, no published price) shows you per-SKU days out of stock, estimated lost sales, and a weekly buying list — the raw material for inputs B, C, and D above — but the width-vs-depth decision stays yours.
Common questions
What is assortment planning? Deciding what your store carries — which categories (width), how much choice within each (depth), and which specific SKUs — before buying. For a small retailer it's the decision that determines whether every downstream reorder point and buy is aimed at the right products. It's usually run as a periodic range review against your own sales data.
Should a small store carry wide or deep? Depth in fewer categories usually wins: it concentrates cash and data on SKUs that forecast well and makes you the credible option in the categories you keep. Width adds customers but each category carries fixed costs and thins your buying power. The practical rule: be deep in everything you keep, or exit the category — the middle of the dial is the expensive position.
How do I run a range review? Quarterly, per category: pull 90 days of sales, revenue, and stock value by SKU; record revenue share, the spread between best and worst sell-through, what share of SKUs makes 80% of sales, out-of-stock days, and inventory value. Read the pattern together — high revenue share with terrible spread means re-cut the picks; low everything means the category's depth is wrong.
How do I know when to add a new product category? When four gates clear: your core categories are already working, you have tested demand (trial SKUs, pre-orders, countable requests), the trial cash doesn't come from proven bestsellers' reorder money, and you've written the exit criteria in advance. Then start deep in the hottest sub-niche, not wide across the category.
What's the difference between assortment planning and SKU rationalization? Assortment planning is the forward decision — what the range should be, including additions. Rationalization is the backward decision — which existing SKUs to cut when the range has drifted too wide. The range review feeds both: it identifies the underperformers that rationalization will evaluate and the demand clusters the new plan should serve.
Next step
Fill in the five-input worksheet for your two largest categories this week — it's a 30-minute export job. If the sell-through spread inside either is worse than about 60 points, you've found next quarter's real project: not a new category, but a re-cut of the depth you already own. And if both look tight, the freed attention is better spent on the buying calendar than on width you haven't tested.