Warehouse slotting is deciding where each product sits, by how often it is picked and how much space it takes. The products picked most per metre of shelf go at waist height, next to the dispatch table. Walking is the largest part of picking, so good slotting cuts the walk first.
This guide sets out the facts that decide a slot and the steps to slot a store room or warehouse. It works them on a Nairobi distributor's eight busiest lines, in Kenya shillings, and shows where ArmPOS gives you the numbers.
Why warehouse slotting matters
Slotting goes after the biggest cost in a warehouse. In Warehouse & Distribution Science, Bartholdi and Hackman of Georgia Tech put order picking at about 55% of warehouse operating costs.
| Activity | Share of order-picking time | What slotting does to it |
|---|---|---|
| Travelling | 55% | Puts the most-picked products nearest dispatch |
| Searching | 15% | Gives every product one fixed, coded place |
| Extracting | 10% | Keeps popular and heavy goods at waist height |
| Paperwork and other | 20% | Little: that is the job of lists and scanning |
Good slotting brings faster picking, fewer wrong items, better use of space and fewer hours to pay for. It needs no new equipment: only figures you already have, and a session of moving stock.
What decides where a product goes
Picks decide first, then space, then weight and the risk of a wrong pick. A pick is one visit to a product's shelf for one order, whatever the quantity taken.
| Fact | The rule | Why |
|---|---|---|
| Picks | More picks, closer to dispatch | Every pick is a walk there and back |
| Space | Rank by picks per metre of shelf, not picks alone | A bulky fast seller can use up the best shelf |
| Weight | Heavy goods at waist height or below, never above the shoulder | Safer, faster lifting |
| Look-alikes | Sizes, strengths and flavours of one product kept apart | Fewer wrong items in orders |
| Ordered together | Products often in the same order side by side | Two picks for one stop |
| Conditions | Cold, locked and hazardous goods go to their zones first | Safety and the label come before speed |
The waist-height shelf is what Bartholdi and Hackman call the golden zone, "from which it is easiest to pick". They also warn against packing every popular product into one spot, because pickers then queue for it.
The look-alike rule is long-standing practice. Their book describes distribution centres for drug stores that "store similar-looking medicines apart to reduce the chance of a picking error".
How to slot a warehouse, step by step
Slotting takes seven steps and a spreadsheet. Step 3, the ranking, is the one that changes the result.
- Count each product's picks for the last 90 days: the number of orders it appeared in, not the units. A carton of 48 soaps sold to one shop is one pick.
- Measure the shelf space each product needs at its usual stock level, in metres of shelf, or pallet places for pallet goods.
- Divide picks by metres, and rank from highest to lowest. This is the inverse of Heskett's cube-per-order index, which Bartholdi and Hackman cite: space divided by picks, lowest first.
- Fill the best zone down the ranking: waist height, nearest dispatch. When it is full, fill the next-nearest shelves, then the high and far ones.
- Apply the exceptions: cold, locked and hazardous goods to their zones, heavy goods low, look-alikes apart, products ordered together side by side.
- Code and label every shelf, record each product's place, and move the stock in one session, outside opening hours.
- Review every month and re-slot every quarter, and before a season such as December or the start of the school year.
For example: slotting a Nairobi distributor's eight busiest lines
For example, a household-goods distributor in Nairobi has 3 metres of waist-height shelf next to its dispatch table. These are its eight busiest lines for one month. The figures are an illustration, not a real business's.
| Product | Picks a month | Shelf needed | Picks per metre | Slot |
|---|---|---|---|---|
| Matches, outers of 10 packs | 750 | 0.25 m | 3,000 | By dispatch |
| Toothpaste 100 g, boxes of 12 | 1,200 | 0.5 m | 2,400 | By dispatch |
| Bar soap, cartons of 48 | 1,500 | 1 m | 1,500 | By dispatch |
| Washing powder 500 g, bales of 20 | 900 | 1.25 m | 720 | By dispatch |
| Cooking oil 1 litre, cartons of 12 | 1,300 | 2 m | 650 | Next aisle |
| Toilet tissue, bales of 10 | 450 | 2 m | 225 | Further back |
| Rice 5 kg, bales of 5 | 300 | 1.5 m | 200 | Further back, bottom shelf |
| Plastic buckets, stacks of 10 | 100 | 1 m | 100 | Far wall, high |
The eight lines take 6,500 picks a month. Cooking oil is the second busiest line, yet it needs 2 metres. The same 2 metres hold matches, toothpaste and washing powder, with 2,850 picks between them against oil's 1,300.
Before slotting, the bulky tissue and buckets sat by the door because they arrived last. The comparison assumes a round trip of 6 metres to the best shelf and 30 metres to anywhere else. It also assumes pickers walk 1 metre a second with a trolley.
| Arrangement | On the 3 metres | Picks from there | Metres walked | Picker hours |
|---|---|---|---|---|
| Bulky lines by the door | Tissue, buckets | 550, or 8.5% | 181,800 | 50.5 |
| Ranked by picks | Soap, cooking oil | 2,800, or 43.1% | 127,800 | 35.5 |
| Ranked by picks per metre | Matches, toothpaste, soap, washing powder | 4,350, or 66.9% | 90,600 | 25.2 |
Ranking by picks per metre saves 91,200 metres of walking a month against the old layout, about 25.3 picker hours. At KES 120 an hour, that is about KES 3,040 a month.
Against ranking by picks alone, it still saves 37,200 metres, or 10.3 hours. In a small store, slotting saves hours rather than fortunes. Its bigger gain is orders out faster at the busy hour.
Warehouse slotting strategies compared
The strategies below are not rivals: most warehouses combine two or three. Ranking by picks per metre decides the order within each zone.
| Strategy | How it works | Use it when |
|---|---|---|
| ABC by picks | A lines, the most picked, nearest dispatch; B in the middle; C furthest away | Always, as the starting point |
| Volume-based | Bulky goods where there is floor or pallet space; small, fast items in bins at hand height | Products vary a lot in size |
| Zones | Areas by type or condition, such as cold, locked or chemicals, with a picker per zone in bigger stores | Some goods need their own conditions |
| Product families | Products often bought together stored side by side | Orders repeat the same mix |
| Seasonal | Seasonal lines moved forward before their season, and back after it | Demand swings by month |
ABC by picks is not the ABC of the 80/20 rule in inventory, which ranks products by the money tied up in them. Money decides how often you count a line; picks decide where it sits.
Signs your warehouse needs re-slotting
Five signs show that the slots no longer match what sells. Each can be checked in a week.
- Slow picking. Orders take longer to pick than they did, with no rise in order size.
- Wrong items in orders. Look-alike products sit side by side, or a product has moved and its label hasn't.
- Wasted space. Empty shelves sit next to overstocked ones, or cartons spill into the aisles.
- Long walks. Pickers cross the store for the best sellers several times an hour.
- Stock piling up in one place and running out in another. The slot sizes no longer match what each line sells.
Do you need slotting software or a WMS?
Not for a store room or a small warehouse. A few hundred lines rank in a spreadsheet in an afternoon, from a sales report you already have.
Slotting software usually comes inside a warehouse management system, which pays off with many pickers and many locations. ERP vs WMS sets out what a WMS adds, and warehouse management covers the seven steps from receiving to dispatch. How goods are stored, on what and under which rules, is in inventory storage.
How to slot your warehouse with ArmPOS
ArmPOS gives you the pick counts and keeps each product's shelf on record. The ranking and the moves are yours, done once a quarter.
- Get the picks. Reports › Top Selling Products ranks products by how many sales they appear in, its Total Sales, for the dates you pick. That count is the picks in step 1 (Sales reports).
- See the lines behind it. The Product sales report lists each product line of each sale, with the quantity, if you want to check a product's orders.
- Code the shelves. In Settings › Warehouse Locations, create a Rack/Location Code for each shelf, such as A1 by dispatch (Your warehouse and its locations).
- Record each product's slot. Fill Internal Location (Rack/Shelf) on the product's Edit page. After a re-slot, Reports › Internal Location Report lists products by location for a final check (Stock reports).
- Count what you moved. Products › Count Stock makes a count sheet for one warehouse and category, and an adjustment corrects any difference (Count and adjust stock).
See what ArmPOS includes for shops and distributors in Kenya.
Frequently asked questions
What is warehouse slotting?
It is deciding where each product is stored, by how often it is picked, how much space it needs and its weight. The products picked most per metre of shelf go nearest dispatch.
What is the golden zone in a warehouse?
The shelves at about waist height, where picking needs the least bending and reaching. Popular and heavy products go there first.
How often should you re-slot a warehouse?
Review the ranking monthly, move stock quarterly, and re-slot before each busy season. Move only the lines whose rank has changed zone.
What is the difference between slotting and putaway?
Slotting decides each product's home in advance. Putaway is the daily job of placing a delivery into that home.
Should slotting use ABC analysis?
Yes, ranked by picks rather than by value. Divide the picks by the shelf space each line needs, so a bulky line doesn't take the best shelf.
Pull last quarter's Top Selling Products, measure each line's shelf, and rank them by picks per metre this week. To get the picks and record every product's shelf, create a free ArmPOS account.
