What Is Fill Rate?
Also known as: order fill rate, line fill rate, item fill rate, service level (fill)
Definition
Fill rate is the percentage of customer demand, measured in units, lines or orders, that is met immediately from available stock without backorder or delay. It measures how much of what customers asked for was actually shipped when requested.
Fill Rate Explained
Fill rate has three common grains. Unit fill rate is units shipped divided by units ordered. Line fill rate is order lines shipped complete divided by total lines. Order fill rate is orders shipped complete divided by total orders. Order fill rate is the harshest because one short line fails the whole order.
It differs from cycle service level, which is the probability of not stocking out during a replenishment cycle. A product can have a 95 percent cycle service level and a 99.5 percent unit fill rate, because most stockouts are small in quantity. Safety stock formulas aimed at a fill rate target use the expected shortage per cycle, not just the stockout probability.
ERPs record the inputs on sales order lines: ordered quantity, shipped quantity and backordered quantity. SyteLine tracks backorders on the customer order line, NetSuite on sales order line quantity committed versus fulfilled, and Infor LN on sales order line delivery status. Whether a backorder counts as unfilled depends on a definition you must write down, for instance fill against request date or against the original line.
Fill rate looks at stock availability, while OTIF also adds the date test. Fill rate is typically the planner's metric (did we have it), and OTIF is the customer's metric (did it arrive when and how we promised).
Why It Matters
- It ties safety stock investment to a customer-facing outcome that sales and finance understand.
- Differentiating line and order fill rate shows how partial shipments hurt multi-line orders.
- It highlights which items cause the most shortages, which guides reorder point and lot size changes.
- It is a standard clause in distributor and retailer supply agreements.
In Practice
Customers order 50,000 units in a month and 48,500 ship from stock, so unit fill rate is 97 percent. Of 1,200 orders, 1,020 shipped complete, giving order fill rate of 85 percent. The gap shows shortages are spread across many orders, so a small number of chronically short items are blocking otherwise complete shipments.
Frequently Asked Questions
What is the fill rate formula?
Units (or lines, or orders) shipped complete from available stock divided by units (or lines, or orders) ordered, multiplied by 100. State which grain you use.
How is fill rate different from service level?
Cycle service level is the probability of no stockout in a replenishment cycle. Fill rate is the share of demand actually met. The two are related but not interchangeable in safety stock calculations.
Do backorders count as filled?
Under a strict definition no. Fill rate counts only what shipped from stock at the time requested. Some companies report a separate backorder fill rate for items shipped later.
Related Terms
OTIF (On-Time In-Full)
OTIF (On-Time In-Full) is the percentage of order lines or orders delivered on the agreed date and in the complete ordered quantity. A line that is late or short counts as a miss, so OTIF is stricter than on-time delivery alone.
Safety Stock
Safety stock is buffer inventory carried above expected demand to protect against variability in demand and supply during replenishment lead time. In ERP it is netted out of available inventory so MRP plans replenishment before the buffer is consumed.
Reorder Point
A reorder point is the inventory level at which a replenishment order is triggered. It equals expected demand during the replenishment lead time plus safety stock, so stock on hand covers usage until the new supply arrives.
ATP (Available to Promise)
ATP (available to promise) is the portion of inventory and scheduled production not yet committed to existing customer orders, calculated by date so order entry can quote a delivery a customer can rely on.
ABC Analysis
ABC analysis is an inventory classification method that ranks items by annual consumption value and groups them into A, B, and C classes, so planning attention, counting frequency, and control effort are concentrated where the money is.
Go Deeper
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AI Inventory Optimization Algorithms for ERP
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SyteLine Demand Forecasting Configuration Guide
Configure SyteLine demand forecasting with statistical models, forecast consumption, demand management parameters, and accuracy measurement for production planning.
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