Most sites end up with the wrong number of lockers because they divide headcount by six and round up. That method produces a cabinet that is too small on Monday morning, half empty by Friday, and impossible to justify at budget review.
The number you actually need is not derived from headcount. It is derived from peak concurrent users — the maximum number of people who need a locked compartment at the same moment — multiplied by how long each of them keeps it. Everything else is arithmetic.
This guide works that arithmetic for four common sites, then converts the answer into cabinets. It applies to any locker format; the bay sizes referenced are the Mecolor 6-door cabinet, but the method is product-agnostic.
The Formula
Three inputs, one output:
lockers needed = peak concurrent users × peak overlap factor
Where peak concurrent users is the headcount present at the busiest moment, and the overlap factor accounts for people who arrive early or leave late and for the fact that not everyone clears their locker on the same day.
In practice, the model needs two more adjustments:
- Dwell multiplier — if people keep items in the locker permanently (a change of clothes, tools), every person present needs their own bay at all times. If they only use it during a shift, a bay can be shared across shifts. Sharing is where most of the savings hide.
- Attrition add-on — plus 10 to 15 percent for new starters, visitors, and the two bays that end up full of abandoned property.
The formula in full:
lockers = (peak concurrent users ÷ shifts sharing a bay) × 1.12
The 1.12 is the attrition allowance. It is the cheapest part of the calculation to get right, because running out of lockers by one is a far worse problem than having one spare.
Worked Example 1: A 40-Person Office
Assume 40 staff, hybrid attendance at about 60 percent on a typical day, three locker-sharing shifts that are not really shifts — most people keep their items in the locker all week.
- Peak concurrent users: 40 × 0.6 = 24 people on site at once. But this is locker storage, not a desk count: the 40 staff each want somewhere to keep a jacket, shoes, and a laptop bag during the days they are in. The relevant peak is not daily attendance, it is total assigned staff, because a hybrid worker still expects their locker on the days they come in and does not want to clear it out.
- Shifts sharing a bay: 1 (hybrid workers cannot share — they would be sharing with someone whose days overlap unpredictably).
- Lockers needed: 40 × 1.12 = 45 bays.
Six 6-door cabinets give 36 bays — not enough. Eight cabinets give 48, which is the right order. Most offices under-provision here precisely because they size to attendance rather than headcount, then discover that people do not vacate.
The saving clause: if the site operates a genuine clean-out policy — lockers emptied Friday, assigned by booking — the requirement drops to about 24 × 1.12 = 27 bays, or five cabinets. That is a policy decision worth 11 bays, and it should be made before the purchase order, not after.
Worked Example 2: A Gym or Fitness Studio
Gyms are the opposite case: high churn, short dwell, and a legal limit on how many people can be in the changing room at once.
- Peak concurrent users: the changing room's fire capacity, not the gym's membership. A studio with 300 members whose class schedule peaks at 24 people per class, with 20 minutes of changing either side, peaks at roughly 24 to 30 people in the room.
- Dwell: 40 minutes total, so a bay turns over 12 to 15 times in an open day.
- Shifts sharing a bay: effectively unlimited — this is pooling, not assignment.
- Lockers needed: 30 people × 1.12 ≈ 34 bays, and that is generous.
A gym with 300 members needs about 30 to 36 bays, or six 6-door cabinets. The mistake gyms make is sizing to membership (300 ÷ 6 = 50 cabinets, absurd) rather than to simultaneous occupancy. The other mistake is not sizing at all, and treating the locker bank as a place to store lost property.
For a gym, ventilation matters more than capacity. Six cabinets of 14.5-inch bays with louver vents, cleared daily, will handle a 300-member studio. Six sealed boxes of the same size will not.
Worked Example 3: A School
Schools have the most predictable pattern and the most common failure.
- Peak concurrent users: one class cohort changing at once — 30 students, typically.
- Dwell: the school day, so bays are assigned per student, not pooled.
- Shifts sharing a bay: 1.
- Lockers needed: 30 × 1.12 = 34 per changing cohort.
But here is the real constraint: schools usually want every student to have a locker, in which case the count is enrolment, not cohort. A 600-student school needs 600 bays — 100 six-door cabinets — and the sensible architecture is not 100 cabinets in one room. It is banks distributed along corridors, which brings in the layout rules below.
The middle path most schools take: assigned lockers for students who need them (sports kit, instruments, devices), pooled lockers for the rest. That usually lands at 25 to 40 percent of enrolment, which for 600 students is 150 to 240 bays, or 25 to 40 cabinets.
Worked Example 4: A Workshop With Three Shifts
Shift work produces the biggest saving and the biggest argument.
- Headcount: 36 across three shifts, 12 per shift.
- Peak concurrent users: 12.
- Shifts sharing a bay: 3 — if and only if the changeover is clean.
- Lockers needed: 12 × 1.12 = 14 bays, or three cabinets.
Three cabinets for 36 staff is correct, and it will be resisted by the workforce, because a shared bay means someone else's boots are in your locker at 6 a.m. The compromise that actually works: everyone gets a personal bay, but the smallest one. Thirty-six 9-door bays in four cabinets is only 12 more bays than the theoretical minimum and removes the daily friction. This is where the tightest bay in the range — 8.8 inches — earns its place, because work boots and PPE fit in 8.8 inches while a backpack does not. Run the numbers both ways and put the decision to the shift supervisors rather than the finance team: the shared-bay version is cheaper, but the personal-bay version is the one that stays in use.
From Bays to Cabinets: The Division That Bites
Once you have a bay count, divide by bays per cabinet and round up. The near-miss cases are the ones that hurt:
Two things to note. Exactly 36 means zero slack — the first new starter creates a problem, which is why the 12 percent allowance exists and why you should not round it away. And the jump from 36 to 42 bays is expensive — the 37-bay site pays for six unusable bays. If your number lands just above a multiple of six, consider mixing formats: five 6-door cabinets plus one 9-door gives 39 bays in six cabinets' worth of wall space, which usually beats seven cabinets. The mix also hedges your sizing risk — if the bay-height assumption turns out wrong for a handful of people, the 9-door unit absorbs them without a second purchase order.
Layout: The Space Nobody Budgets For
A cabinet is 35.4 inches wide and 15.7 inches deep. The space it needs is much larger than the space it occupies.
Aisle width. A locker bank needs a clear aisle in front equal to the depth of an open door plus a person standing at it. Plan 36 inches minimum, 42 if two people will pass. In a changing room with a bench, add the bench depth and 30 inches of sit-and-stand space in front of it.
Door swing. Six doors on one cabinet all open into the same aisle. If cabinets sit back to back, both banks need their own aisle; if they face a wall, the bank is unusable.
Wall fixing. Every cabinet should be anchored. That constrains placement to walls with studs or masonry behind them — not to a partition wall or the back of a demountable cubicle.
Clear egress. Lockers cannot encroach on an exit route. In corridors, the projection matters: a 15.7-inch-deep cabinet leaves considerably more clear width than a 17.7-inch one, and in a narrow corridor that 2 inches is the difference between compliant and not.
Layout arithmetic for a room: for a bank along one wall, usable cabinets = floor((wall length − 12 inches end clearance) ÷ 35.4). A 20-foot wall (240 inches) takes six cabinets with 36 inches to spare. A 12-foot wall (144 inches) takes three, and the leftover 38 inches is not enough for a fourth.
Accessibility. At least one bay should be reachable at an accessible height and approach — not the bottom row behind an open door. If the lockers serve staff with mobility needs, place the assigned bay in the middle row and keep the approach clear.
What Breaks the Model
The arithmetic is honest, but five real-world factors move the number, and each has a policy answer:
- Hybrid work. Attendance-based sizing undercounts, because assigned lockers do not churn. Size to headcount, or run a clean-out policy.
- Seasonality. A ski resort, a summer camp, a tax office — all peak at a few weeks a year. Size to the peak week, or rent the overflow.
- Visitors and contractors. They need a bay for a few hours and should not take an assigned one. Hold 5 to 10 percent back as a visitor bank.
- Abandoned property. Every locker bank accumulates it. A written 30-day notice-and-clear policy converts dead bays back into usable ones; without it, budget 5 percent as lost.
- Growth. A site hiring 20 percent next year needs 20 percent more bays next year. Where the wall space exists, buy one cabinet spare; where it does not, plan the second bank now.
Choosing the Format After the Count
The count tells you how many bays. The contents tell you which format.
Then apply the two specs that decide whether the site tolerates the cabinet: ventilation if anything goes in damp, and lock ownership — padlock latches mean users bring their own locks and the site never manages a key register. Bay count without the right bay height produces a cabinet that is correctly sized and still unused, which is the most expensive outcome available.
Frequently Asked Questions
How many lockers do I need per employee?
One bay per employee is the safe default, because assigned lockers do not churn even when attendance is part-time. The exception is genuine shift work with clean changeovers, where three shifts can share one bay — 36 staff across three shifts need about 14 bays, though most sites give everyone a personal bay and use the smallest format instead.
Should I count headcount or daily attendance?
Headcount, for assigned lockers. Attendance-based counts work only if lockers are pooled and cleared daily. Hybrid offices that size to attendance end up short, because the person who is in two days a week still holds their locker the other three.
How many bays does one cabinet give?
A 6-door cabinet gives six bays at roughly 14.5 inches high; a 9-door gives nine at about 8.8 inches; a 2-door vertical gives two at about 15.7 inches. The number you divide by has to match the format you are actually buying.
What aisle width do lockers need?
36 inches minimum in front of the bank, 42 inches where two people pass, measured from the cabinet face with doors open. Add bench depth and standing space if the bank faces a bench in a changing room.
How many lockers does a gym need?
Size to changing-room occupancy, not membership. A studio with 300 members whose classes peak at 24 to 30 people in the room needs about 30 to 36 bays — six cabinets — because bays turn over 12 to 15 times a day.
What if my bay count lands just above a multiple of six?
Mix formats instead of buying another cabinet. Five 6-door cabinets plus one 9-door gives 39 bays in the wall space of six cabinets, which is usually cheaper than a seventh cabinet and uses space you did not have.
Do I need to add a margin?
Yes — 10 to 15 percent, for new starters, visitors, and abandoned property. Running out of lockers by one is worse than one spare, and a written clean-out policy is what keeps the margin from turning into permanent overflow.
Does this calculation work for padlock-style lockers?
Yes. The count is independent of the lock type. Lock type affects operations, not capacity: padlock latches mean users supply their own locks and the site keeps no key register, which is simpler for shared and high-turnover sites.
Turn the count into a purchase. The Mecolor 6-Door Metal Storage Locker supplies six 14.5-inch bays per 35.4-inch footprint at $209, with padlock-compatible latches, louver vents, and card slots — free US shipping in 3–7 business days. Tell us your peak concurrent users and bay height requirement, and the US warehouse collection covers the rest of the range.
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