Fill Rate Calculator
Measure how much demand you actually meet from stock. Fill rate is the fraction of demand satisfied immediately from inventory, a direct, customer-facing service metric that complements the cycle service level used to set safety stock.
Calculate Fill Rate →What is Fill Rate?
Fill rate is the proportion of customer demand that is satisfied directly from available stock, without backorder or delay. It is one of the most customer-relevant service metrics, because it measures the share of demand actually met rather than the probability of avoiding a stockout.
Fill rate can be measured in different ways. Unit fill rate is the fraction of demanded units supplied from stock; order (or line) fill rate is the fraction of orders (or order lines) filled completely. These can differ substantially: a warehouse might supply 98 percent of units but fill only 90 percent of orders completely, because a single missing item makes a whole order incomplete.
It is important to distinguish fill rate from cycle service level. Cycle service level is the probability of not stocking out during a replenishment cycle, an event-based measure used to set safety stock. Fill rate is a quantity-based measure of how much demand is met. Two systems with the same cycle service level can have very different fill rates depending on the size of shortages when they occur.
In plain terms: Fill rate answers: of everything customers wanted, how much did we actually give them straight from the shelf? You can measure it by units or by whole orders, and they differ, one missing item can make a whole order 'unfilled'. It's not the same as service level, which is about how often you avoid running out at all.
Ways to Measure It
Unit Fill Rate
The fraction of demanded units supplied from stock. The most common quantity-based measure.
Order / Line Fill Rate
The fraction of orders or order lines filled completely. Stricter, since one missing item fails the whole order.
Not the Service Level
Fill rate measures how much demand is met; cycle service level measures how often a stockout is avoided. They differ.
Key Formulas
Reading Fill Rate
Fill rate directly reflects the customer experience: an 97% unit fill rate means 3% of demanded units were not available when wanted. Because it captures the magnitude of shortages, it is often a better service target than cycle service level for customer-facing commitments.
Choose the fill-rate definition that matches how customers experience service. If complete orders matter (a customer needs all items to proceed), order fill rate is the right measure; if partial shipments are acceptable, unit fill rate is appropriate. Reporting the wrong one can overstate the service customers actually feel.
Assumptions & Validation
Measured Demand & Supply
Total demand and the amount supplied from stock are recorded.
If violated: Capture unmet as well as met demand; lost sales are easily missed.
Right Definition
The fill-rate measure (unit vs order) matches the service question.
If violated: Use order fill rate when complete orders matter.
Consistent Period
Fill rate is measured over a consistent period.
If violated: Compare like periods to avoid seasonal distortion.
⚠️ Check assumptions first
Fill rate is only accurate if unmet demand is actually captured; lost sales that walk away unrecorded make fill rate look better than it is. Choose the definition, unit or order fill rate, that matches how customers experience service, since they can differ widely. And do not confuse fill rate with cycle service level: the same service level can correspond to very different fill rates depending on shortage sizes.
When NOT to Use Fill Rate Calculator
Setting Safety Stock
To size safety stock, the cycle service level and its service factor are the direct inputs.
Order Timing
To decide when to reorder, use the reorder point, not fill rate.
Order Quantity
To decide how much to order, use the EOQ.
Industry Applications
Service Measurement
Track the share of demand met from stock as a customer-facing KPI.
Service-Level Agreements
Set and monitor fill-rate commitments in supply agreements.
Inventory Performance
Assess how well inventory policy translates into met demand.
Trade-off Analysis
Relate fill-rate targets to the inventory investment they require.
Frequently Asked Questions
What is fill rate?
Fill rate is the proportion of customer demand satisfied directly from available stock, without backorder or delay. It measures how much demand is actually met rather than the probability of avoiding a stockout, making it a highly customer-relevant service metric. Fill rate can be measured by units supplied or by orders filled completely, and these two definitions can give noticeably different results.
What is the difference between unit fill rate and order fill rate?
Unit fill rate is the fraction of demanded units supplied from stock, while order fill rate is the fraction of orders filled completely. Order fill rate is stricter, because a single missing item makes an entire order incomplete. A warehouse might achieve a high unit fill rate yet a lower order fill rate, so the right measure depends on whether customers need complete orders or accept partial shipments.
How is fill rate different from service level?
Cycle service level is the probability of not stocking out during a replenishment cycle, an event-based measure used to set safety stock. Fill rate is a quantity-based measure of how much demand is met from stock. Two systems with the same cycle service level can have very different fill rates, because service level ignores the size of shortages while fill rate captures it. They answer different service questions.
Why can fill rate be misleading if lost sales aren't tracked?
Fill rate compares demand met against total demand, so it depends on measuring unmet demand accurately. When customers who cannot get an item simply leave without recording the demand, those lost sales are invisible, and the fill rate appears higher than the true service customers experienced. Capturing unmet demand, not just fulfilled demand, is essential for an accurate fill-rate figure.
Which fill-rate measure should I use?
Use the measure that matches how customers experience service. If customers need all items in an order to proceed, order or line fill rate reflects their experience best. If partial shipments are acceptable and each unit has independent value, unit fill rate is appropriate. Reporting the wrong measure can overstate service, so aligning the definition with customer needs is important.
How does fill rate relate to inventory investment?
Higher fill-rate targets generally require more inventory, particularly more safety stock, and the relationship is nonlinear: pushing fill rate toward 100 percent becomes increasingly expensive. Understanding this trade-off lets a business set fill-rate targets that balance customer service against inventory cost, often differentiating targets by item importance rather than applying a single high target across the board.
Measure the Demand You Actually Meet
Calculate unit or order fill rate as a customer-facing service metric. Free during Beta.
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