What Is Fill Rate? Definition and How to Calculate It

What is fill rate?

Fill rate is the percentage of ordered demand that you ship from inventory on hand, at the time the order is due, without a backorder or a substitution. It is an outcome measure: it tells you how much of the demand you actually received was met.

For example, a customer orders 100 units and you ship 85 from stock. The unit fill rate on that order is 85%. The other 15 units were backordered, cancelled or substituted, and which of those happened matters to the customer but not to the calculation.

Fill rate is reported by SKU, by customer, by channel and by warehouse. A CPG brand or manufacturer selling into retail, wholesale and DTC usually needs it at all four levels, because a healthy company-wide number can hide one retail account that is being shorted every week.

How do you calculate fill rate?

There are three standard formulas, and a fourth that retailers use. Each one answers a slightly different question.

Unit and case fill rate

Unit fill rate is the volumetric measure. It gives partial credit for a partial shipment, so a small shortfall on a large order barely moves it. Case fill rate is the same calculation in cases, and it is the version that matters on a retail purchase order, which is written in cases.

Line fill rate

Line fill rate counts each order line, meaning one SKU on one order, as either complete or not. A line short by one unit counts as a miss. It is a good operational measure for a distribution centre, because it tracks how often a picker went to a location and found too little.

Order fill rate

Order fill rate counts an order as filled only if every line shipped complete. It is the strictest version and the closest to what the customer experiences. It is also the most sensitive to order size: the more lines a typical order carries, the more chances one of them has to come up short.

How do the three versions compare on the same orders?

Running all three on the same set of orders shows why the version has to be named whenever a fill rate is quoted.

For example, from that table:

• Unit fill rate = 385 ÷ 450 = 85.6%
• Line fill rate = 13 ÷ 15 = 86.7%
• Order fill rate = 3 ÷ 5 = 60%

For example, the same week of shipping reads as 86% or 60% depending on which formula is used. Two short lines on two large orders cost 15% of the volume but 40% of the orders.

Which fill rate do retailers measure?

Retail compliance programs measure delivery against each purchase order, and the in-full half of that measure is a case fill rate. Walmart's on-time, in-full (OTIF) program is the best-known example. Its in-full goal is 95%, measured as cases ordered against cases delivered, and suppliers that miss the goal are fined 3% cost of goods on the cases that did not meet it.

Two things follow for a planner:

• The scorecard counts every short case. One deep stockout on a large purchase order can cost more than several shallow ones, even if your internal unit fill rate looks healthy.
• Allocation decides who sees the miss. When a SKU is short across several open orders, how the available cases are split decides which account's scorecard takes the hit.

Each retailer publishes its own definition, target and chargeback schedule. How to avoid retail chargebacks covers the compliance side, including the delivery windows behind the on-time half.

How is fill rate different from service level?

Cycle service level is the share of replenishment cycles that end without a stockout. A cycle that runs short by one unit counts as a failure, exactly like one that runs short by a thousand. Fill rate counts the units, lines or orders actually missed, so it reflects how large each shortfall was.

The distinction matters because the standard safety stock formula targets cycle service level, while customers and retailers judge you on fill rate. A SKU can hold a high cycle service level and still fail an in-full target if its stockouts, though rare, are deep and land on large retail orders. Service level vs fill rate works through both metrics on the same inventory and shows how safety stock is sized to each.

What lowers fill rate, and how do you raise it?

Low fill rate is a symptom. Find which SKUs and which orders account for the missed units before changing anything, because the fix depends on the cause.

• Forecast misses. Demand ran above forecast for longer than the safety stock covered. Look at forecast error by SKU and channel, not in aggregate.
• Safety stock sized to the wrong target. Buffers set as a flat number of weeks of supply are too thin on volatile SKUs and too thick on steady ones. What is safety stock covers sizing it from demand variability instead.
• Late or short supplier deliveries. Track supplier on-time and in-full the same way your retailers track you.
• Reorder points that have not kept up. A reorder point set last year does not reflect this year's lead times or volumes. Target inventory vs safety stock shows how the reorder point is built from its parts.
• Allocation by order date alone. When stock is short, decide in advance which accounts are protected first.

Raising fill rate by adding stock everywhere is expensive. Reducing dead stock without killing fill rate covers moving the buffer to the SKUs where a miss costs most.

Common calculation mistakes

• Quoting a fill rate without naming the version. A fill rate means little until someone says whether it was counted in units, cases, lines or orders.
• Counting backorders as filled. Decide whether a unit that ships late counts, and apply the rule everywhere. Most retail scorecards do not count it. What is a backorder covers the accounting.
• Measuring against shipped orders instead of ordered quantities. If a customer cuts an order because you warned them you were short, that cut is still missed demand.
• A fill rate above one hundred percent. Units shipped cannot exceed units ordered on the same order. A result above it means shipments are being matched to the wrong orders.

Where Planster fits

Planster converts the safety stock you set for each SKU, in days of cover, into units from the forecast, nets the forecast against stock on hand and on order, and recalculates reorder points as lead times and the forecast change. Purchase orders are drafted for your team to approve. See reorder recommendations for how the calculation runs.

Planster has no prebuilt fill-rate or OTIF report; reporting is custom. Measure fill rate from your shipment and retailer scorecard data, and use the result to decide which SKUs need more days of cover. The agent can help you calculate how many.