Pick face sizing: how deep each forward-pick bin should be

Most picking delays in a small stockroom come from one design flaw: the spot you pick from holds too little stock, so you refill it mid-shift, or too much, so half the shelf sleeps. The fix is arithmetic, not hustle. A pick face is the single location you pick a SKU from, and sizing it follows one rule: hold one to two refill cycles of demand at the face, round up to whole case packs, and keep everything else in reserve. Below: the face-depth math, a worked example with illustrative numbers, refill triggers, and the rules for deepening a face versus pulling from reserve.

What a pick face is (and isn't)

A pick face is the forward-facing spot — one bin, one shelf section — from which every unit of a SKU gets picked during normal order flow. The collection of faces is the forward pick area, which the ASCM Dictionary defines as storage staged for picking rather than bulk replenishment (ASCM Dictionary, accessed November 2026). Reserve, or backstock, is everything behind it — it refills faces and holds stock between purchase orders; picks touch it only in abnormal flow.

Walking to reserve mid-pick is expensive: order picking is generally the largest single component of warehouse operating cost, much of it walking (Edward Frazelle, World-Class Warehousing and Material Handling, accessed November 2026). A face sized to absorb a day of picks keeps the picker at the shelf.

Two neighboring jobs sit outside this article: how bins get named and coded (bin location labeling guide) and where each SKU's face belongs on the wall (warehouse slotting guide). This article takes both as given and sizes what sits inside each face.

The face-depth math, in one formula

Face depth = daily velocity × (days between refills + 1), rounded up to whole case packs

Each input, briefly:

• Daily velocity. Units sold per day per SKU, averaged over a recent period when the SKU was actually available. A month of Shopify sales data is plenty for this decision.
• Days between refills. Your cadence. Most two-person operations refill every morning; anything past three days for a SKU moving above 2 units a day is asking for empty bins.
• The +1 cushion. One extra day of demand so a face refilled at 8am doesn't go dry at 4pm. Case-pack rounding often supplies it for free — you can't stock 12 units when cartons hold 10, so you round to 20.
• Case pack. Faces refill in cartons, not units, so the case pack is the smallest legal increment of face depth.

Size is also height: the fastest faces belong at waist height, where picking is quickest and lifting is safest (Gwynne Richards, Warehouse Management, accessed November 2026).

A worked sizing example with illustrative numbers

Four SKUs from a 40-SKU stockroom, with the kind of numbers a sub-$2M store actually has. Refill runs every morning for anything moving 3+ units a day, weekly for the tail:

The enamel pin is the limit case: one tray holds about 24 days of cover, so the tray is face and reserve at once. SKUs this slow don't earn a dedicated face — the tray lives in a shared small-parts bin, topped up weekly.

These numbers imply the split. Say on-hand across the four SKUs is 120 stands, 90 socks, 66 lights, and 140 pins — 416 units, two weeks of cover each. Forward: 16 + 10 + 6 + 24 = 56 units, about 14% of stock, serving 100% of picks. All illustrative — set the benchmark from your own data — but the shape is the point: the front 15% of your units does nearly all the work.

When to deepen a face versus pull from reserve

Faces drift out of size as velocity drifts. Symptoms, and the fix each calls for:

Worked through: the stands jump to 9 units a day in Q4. Two cycles is 9 × 2 = 18, rounding to 3 cartons (24) — a one-carton deepening, no new shelf. If the face still empties before the morning refill, hold two full cycles: 9 × 3 = 27, rounding to 4 cartons (32). Come January, walk it back down.

Deepening is the cheap direction: an extra carton deep on an existing shelf costs inches, while a new bay of starter steel shelving runs an estimated $150–$300 (illustrative retail pricing, as of November 2026). Deepen first; buy steel only when width, not depth, is what's short.

Bridge face and reserve with a habit: keep one full reserve case directly behind or above each fast face. When the face empties, swap the cases; the empty carton is the refill signal. No app needed — just the discipline of the same spot every time.

Replenishment triggers that survive a busy week

A sized face still needs a trigger. Four that work at small scale:

• Fixed schedule. Every face gets topped up at the same time each morning, plus a midday sweep in peak season. Cheapest to run; fails when a SKU accelerates.
• Two-bin. One case at the face, one behind it; the empty case is the trigger. Self-correcting and system-free — the full mechanics are in our two-bin system guide.
• Min/max on the face. Set a trigger at one cycle of demand (12 units for the stands); refill when the face count drops below it. In Shopify, a saved view filtered on available quantity shows these at a glance — there is no native low-stock email alert, so saved views plus Shopify Flow notifications are the built-in options (Shopify Help Center, accessed November 2026).
• Tape-line. A marked fill line inside open bins; stock below the line means refill. Useful for loose stock like socks, where cartons don't map to bin shape.

Triggers assume the face count is trustworthy. Weekly counts of the fast faces keep them accurate; Shopify's native counts carry a planned date, not a recurrence, so the weekly cadence is a calendar entry you own (Shopify Help Center, accessed November 2026).

How much stock belongs forward versus in reserve

The heuristic: forward holds what you'll sell between refills plus the cushion — nothing more. Reserve holds the rest: the depth that carries you between purchase orders. In the worked example that put about 14% of units forward. Your number moves with receiving frequency: weekly domestic deliveries let faces run shallow; monthly container receipts deepen face and reserve alike.

For a one-room operation the deeper question is whether to keep reserve at all — some small stores let the sales-floor shelf be the face. That trade-off, and when each side wins, is covered in our floor stock vs backstock guide.

One Shopify note: with a single location, Shopify shows one available quantity per SKU — it can't see the face/reserve split. The split lives physically, in bin labels and the habit that picks touch the face only, which is what keeps the system number and shelf number agreeing.

Sizing mistakes that show up by week three

• Sizing once and never again. Velocities drift with seasons and campaigns; re-run the math quarterly, or when a face empties early twice in one week.
• Giving every SKU a face. The tail that moves under roughly one pick a week costs more shelf than it saves. Pick it from reserve or a shared bin — the pins are the model.
• Sizing by units and ignoring cube. A yoga mat face is one unit wide and two feet tall; a pin tray is 24 units in six inches. Compare faces in shelf-inches per day of cover, not unit counts.
• Letting face and reserve mix. The moment pickers grab from the nearest carton, the face stops being a face and every count becomes a surprise; the case-behind-the-face habit is the cheapest prevention.

Next step

Today, take your five fastest SKUs and run the one-line math: daily velocity × 2, rounded up to case packs. Check whether each bin actually holds that much; where it doesn't, deepen the face and stand one reserve case behind it. Naming face and reserve bins so pickers can tell them apart is covered in the bin location labeling guide.