Supplier service level: measure it before you suffer it

Two suppliers, two major names in the trade, near-identical catalogs. One delivers ninety-two to ninety-three percent of what you order. The other is under fifty. The second forces its customer to carry twice the inventory, and that extra cost appears on no invoice.

"Service level" covers three different measures#

This is the first source of misunderstanding, including inside a single company: the buyer and the finance director aren't talking about the same indicator, and are surprised not to agree.

What is service level by quantity?#

Quantity delivered ÷ quantity ordered. This is the one that sizes your inventory, because it says how much is missing when the pallet arrives.

Punctuality#

Orders arriving on the promised date ÷ total orders. This is the one that sizes your planning and your commitments to customers.

OTIF, the hardest and the most honest#

On time in full: the share of orders delivered complete and on time.

A supplier can show ninety-five percent on dates and sixty percent on quantity: they deliver on time, but they deliver half. If you only track the first figure, you'll never understand why your shelves keep emptying.

The formula, and the trap inside it#

Line by line, over a given period:

service level by quantity = Σ quantities received ÷ Σ quantities ordered

Defensive over-ordering falsifies everything#

The trap is in the denominator. If your buyers have got into the habit of ordering twenty percent more "because he'll only deliver eighty anyway", your calculated service level rises artificially, and you lose the information. Defensive over-ordering is the main falsifier of this indicator, and it is almost always in place without anyone having decided it.

How do you stop over-ordering falsifying the figure?#

1. Measure against the initial order, not the order as corrected after negotiation.
2. Compare the quantity received to the quantity you actually wanted — the one the replenishment calculation proposed before any human intervention.

If the gap between the two is wide, you already have an answer: your teams have been compensating for a long time, quietly.

We knew he delivered badly. We didn't know it was one order in two.

Why a supplier delivers badly, and why it can sometimes be fixed#

It's worth looking for the cause before drawing conclusions, because a poor service level is often organizational rather than structural.

The causes we see again and again:

You are attached to the wrong entity#

A French customer served by a group's Spanish export subsidiary, because that's the box they historically fell into, has neither the same catalog nor the same priority as one served by the French logistics operation.

The supplier has no platform, but plants#

They consolidate your order from three sites before shipping. Every missing line delays the whole order.

Setting up a new product takes weeks#

It takes weeks in their system before it can be shipped even once.

None of these three causes is visible from your ERP. All three become visible when you call their key account manager with your figures in hand — and that's where measurement earns its keep: it turns a complaint into a negotiation.

What the number should change, in practice#

A supplier service level isn't there to produce a league table. It's there for three decisions:

It sets your safety stock#

A supplier at fifty percent mechanically forces you to carry more, and that "more" can be calculated. It is that supplier's real cost, to be added to their purchase price before any comparison.

It opens the commercial conversation#

A supplier shown twelve months of their own deliveries, line by line, no longer argues the same way. We've seen logistics arrangements change on the strength of a single table.

It settles dual sourcing#

On a critical item, the question isn't "who's cheapest" but "who costs me least, safety stock included".

Measuring it without spending your days on it#

There is nothing complicated about this calculation. It's simply tedious to maintain by hand, which is why almost nobody maintains it.

The three pieces of data you already have#

It needs order lines, receipt lines, and the dates of both. Everything else is arithmetic. In the applications we build, it fits on one page: one supplier per row, their fill rate, their punctuality, their OTIF, and a twelve-month curve to show whether it's improving or slipping.

What alert should you set on a service level?#

It is the change: a supplier who goes from ninety to seventy-five percent in two months has a problem you want to know about before your customers do.

How we measure it without spending time on it#

Service level is not measured by hand: it is measured at goods receipt, and only once. Every packing slip is compared line by line against the order, and the gap is recorded with its date.

After a quarter you have quantity, timing and OTIF per supplier, without a spreadsheet ever being opened. That is the figure you put on the table at renegotiation. See the orders and packing slips module.

Supplier service level: what to remember#

Measure it by quantity, by date and as OTIF: those are three different realities, and the third is the one your end customer experiences.

Calculate it against the order you wanted to place, not the one you've learned to place. The gap between the two is often the first interesting figure of the whole exercise.

And remember that a badly rated supplier isn't necessarily a bad supplier: sometimes it's a supplier nobody has yet shown their own numbers to.