Fill rate measures the share of demand you supplied completely from stock on hand, without a shortfall, a substitution or a backorder. Receive orders for 1,000 units and ship 940 of them from available stock, and your fill rate is 94%.
Fill rate = (units or orders supplied in full ÷ units or orders ordered) × 100
The word doing the work is completely. Fill rate is about completeness, not timing — an order shipped complete three weeks late counts as filled. That is the distinction from OTIF, which requires both, and it is why the two figures always differ.
What fill rate is
Fill rate answers one question: when customers asked, could you supply?
It measures availability at the moment of demand. Not whether you eventually supplied, and not whether you had stock last week. Whether the stock was there when the order arrived.
It is the customer-facing counterpart of a stockout. A stockout is the event; fill rate is the measure of how often events like it occur across all your demand.
It is calculated at whatever level you choose — orders, lines, units or cases — and the level changes the number substantially. That is the main reason fill rate figures from different sources are hard to compare, and it is covered below.
What it deliberately excludes. Timing. A supplier with a 98% fill rate and a habit of shipping a week late looks excellent on this measure and poor to the customer. Fill rate is one half of a picture and should never be the only measure quoted.
The fill rate formula and a worked example
Fill rate = (quantity supplied ÷ quantity ordered) × 100
A distributor reviews a month.
The figures:
- Total order lines received: 2,400
- Lines shipped complete from stock: 2,208
- Total units ordered: 31,500
- Total units shipped: 30,555
- Total orders received: 640
- Orders shipped complete: 544
Line fill rate:
(2,208 ÷ 2,400) × 100 = 92.0%
Unit fill rate:
(30,555 ÷ 31,500) × 100 = 97.0%
Order fill rate:
(544 ÷ 640) × 100 = 85.0%
Three numbers from the same month, ranging from 85% to 97%. None is wrong; they measure different things.
Unit fill rate is the most forgiving, because a shortfall of two units on a line of two hundred barely registers.
Order fill rate is the strictest, because one short line fails the entire order however complete the rest of it was.
Line fill rate sits between them and is usually the most diagnostic, because it tells you how many individual product requests you failed rather than how many units or how many orders.
The practical rule. Order fill rate reflects what the customer experiences. Line fill rate tells you where to look. Pick one as your headline measure, state which it is, and never compare your figure with somebody else’s without establishing that they used the same basis.
The types of fill rate
| Type | What it measures | Formula | Best for |
|---|---|---|---|
| Order fill rate | Orders shipped complete | Complete orders ÷ total orders | The customer’s actual experience |
| Line fill rate | Order lines shipped complete | Complete lines ÷ total lines | Diagnosis — which products are failing |
| Unit fill rate | Units shipped against units ordered | Units shipped ÷ units ordered | Volume-based supply performance |
| Case fill rate | Cases supplied against cases ordered | Cases shipped ÷ cases ordered | Wholesale and retail supply |
| SKU fill rate | Availability of a specific product | Units of that SKU shipped ÷ ordered | Identifying problem products |
| Warehouse fill rate | What one site could supply | Supplied by that site ÷ demanded of it | Comparing locations in a network |
| Vendor or supplier fill rate | What your supplier delivered to you | Units received ÷ units ordered | Upstream performance, and the root of most downstream failures |
Supplier fill rate deserves particular attention. You cannot ship in full what you did not receive, and measuring the same metric upstream frequently reveals that a customer-facing problem originates with two or three suppliers rather than with your own operation. It is the single most useful addition for most businesses, and the one most often missing.
Fill rate vs service level vs in-stock rate vs backorder rate
These four overlap enough to be used interchangeably, which causes real confusion in supplier conversations.
Fill rate is what actually happened — the measured share of demand supplied complete.
Service level is a target you set in advance, usually as a probability: a 95% service level means sizing safety stock so that demand is expected to be met in 95% of replenishment cycles. It is an input to a calculation; fill rate is an output of the operation. They are related and not the same, and a 95% service level does not produce exactly a 95% fill rate.
In-stock rate measures availability over time rather than against demand — the share of time a product was available. A product out of stock for two days in a slow month scores badly here and may have missed almost no demand, which makes in-stock rate more useful in retail shelf terms than in supply terms.
Backorder rate is the share of demand that was not filled and was converted into a promise to supply later. It is roughly the complement of fill rate for businesses that accept backorders, and it says nothing about whether the customer eventually received the goods or cancelled.
And OTIF requires both completeness and timing on the same order. It is always lower than fill rate, because fill rate ignores the timing half entirely.
A practical way to hold them apart: service level is what you planned for, fill rate is what you delivered, in-stock rate is how often the shelf had it, backorder rate is what happened to the rest, and OTIF is whether the customer got it complete and on time.
Why fill rate matters
It is the measure customers actually feel. A short delivery is a problem the customer has to solve — chasing, reordering, or buying elsewhere.
It quantifies lost sales. Every point of fill rate below 100% is demand you saw and did not serve, which is far better information than a stockout that leaves no trace.
It is contractual in retail supply. Major retailers set supplier fill rate requirements with financial penalties attached, deducted rather than invoiced. For anyone supplying them, this is a commercial measure before it is an operational one.
It diagnoses the in-full half of OTIF. Where OTIF is failing, splitting it into on-time and in-full immediately tells you whether the problem sits with stock availability or with dispatch timing — different causes with different owners.
It prices the safety stock decision. Moving fill rate from 95% to 98% requires a calculable amount of additional stock. Setting that against the value of the demand it captures turns a service question into a commercial one.
It measures suppliers objectively. Applied upstream, it replaces impressions about reliability with a number.
Common causes of low fill rate
Reorder points set from quoted lead times rather than measured ones. The most common single cause, and the cheapest to fix.
Safety stock too thin on lines where demand or supply varies. Frequently the result of applying one rule across a whole range instead of sizing per product class.
Forecast error, particularly around promotions, launches and seasonal peaks where there is little history.
Supplier shortfalls passed straight through. Your supplier’s fill rate becomes yours.
Inventory inaccuracy. Orders accepted against phantom stock, which produces a short shipment and an apology rather than a clean refusal at the point of order.
Replenishment failure. Stock in reserve, pick face empty, order shipped short whilst the goods were in the building.
Allocation problems. Stock committed to other orders without the system reflecting it, so availability looks higher than it is.
Range proliferation. More variants spreading the same demand, each needing its own buffer, with buffers rarely resized to match.
Cash constraints. The stock was needed and the money was not there — a cause that operations teams cannot fix and should still record honestly.
How to improve your fill rate
Fix reorder points first. Calculate them from measured supplier lead times, using your last twenty receipts. This single change addresses more availability failure than anything else and costs nothing but the effort of pulling the dates.
Size safety stock from real variability, per product class, at a service level you have chosen deliberately. Not a uniform number of weeks applied to everything.
Measure your suppliers’ fill rate and act on it. You cannot supply what you did not receive. Two or three suppliers frequently account for most of a fill rate problem.
Fix inventory record accuracy. Phantom stock produces the worst kind of fill rate failure, because you accepted the order first.
Watch the pick face. Replenishment triggers deserve the same attention as reorder points, and an empty pick face above full reserve stock is entirely self-inflicted.
Prioritise by consequence. Your top lines and anything customers come to you specifically for warrant high fill rates. A slow-moving item with easy substitutes does not, and holding buffer for it is money doing nothing.
Exclude stockout periods from demand history. Otherwise your forecast learns that demand is lower than it is, on the very products that already failed.
Offer substitutes actively where the product allows it. A customer shown an alternative converts far more often than one left to find their own, and it is a merchandising decision that has to be made in advance.
Record why every failure happened, using a fixed list of causes. A month of coded failures usually points at one or two fixable things, which is more useful than knowing the percentage.
Report it at line level alongside order level, and alongside on-time performance. A single aggregate number tells you that you have a problem and nothing about where it is.
Where to go deeper
- What is OTIF — completeness plus timing together.
- What is a stockout — the individual failure fill rate aggregates.
- What is safety stock — the buffer that sets your achievable fill rate.
- What is a reorder point — the trigger that most often causes failures.
- What is a backorder — what unfilled demand becomes when customers wait.
- Warehouse KPIs — where fill rate sits among the measures.
The one-line takeaway
Fill rate is the share of demand you supplied complete from stock, measured by order, line or unit — and the level you choose changes the number substantially, so state it. It ignores timing entirely, which is why it must be read alongside on-time performance, and most of the fixing is done at reorder points and supplier measurement rather than by holding more stock everywhere.
Frequently asked questions
What is fill rate? The percentage of demand supplied completely from stock on hand, without shortfall, substitution or backorder. It measures completeness only — an order shipped complete but late still counts as filled, which is the key difference from OTIF.
How do you calculate fill rate? Divide the quantity supplied by the quantity ordered and multiply by 100. The quantity can be orders, lines, units or cases, and each gives a noticeably different figure from the same data — order fill rate is strictest, unit fill rate most forgiving, line fill rate usually most diagnostic.
What is the difference between fill rate and service level? Service level is a target set in advance, expressed as a probability and used to size safety stock. Fill rate is what actually happened, measured after the fact. They are related and not equal — a 95% service level does not produce exactly a 95% fill rate.
What is a good fill rate? It depends on sector and on how it is measured. Major retailers commonly require supplier fill rates in the mid to high nineties with financial penalties below that. More useful than any benchmark is your own trend, the split between products, and whether the cost of the next percentage point is worth what it captures.
What is the difference between fill rate and OTIF? Fill rate measures completeness only. OTIF requires completeness and timeliness on the same order, so it is always the lower of the two. Where OTIF is failing, splitting it into on-time and in-full shows immediately whether the problem is stock availability or dispatch timing.
What is supplier fill rate? The same measure applied upstream — what your supplier actually delivered against what you ordered. It is frequently the root of a customer-facing fill rate problem, since you cannot ship in full what you did not receive, and it is the measure most often missing from a business’s reporting.
How do I improve fill rate? Recalculate reorder points from measured rather than quoted supplier lead times, size safety stock from actual demand and lead time variability per product class, measure and manage supplier fill rate, fix inventory record accuracy so you stop accepting orders against phantom stock, and make sure the pick face is replenished before it empties.
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