Your customer orders 100 units. You ship 85. What happened to the other 15?
Fill rate measures this gap—the difference between what customers want and what you can actually deliver from available inventory.
Fill Rate Definition
Fill rate is the percentage of customer demand that you fulfill from stock on hand. It measures how often you have the right products available when customers want to buy them.
A 95% fill rate means you successfully fulfill 95% of what customers order. The other 5% is backordered, substituted, or lost.
Why Fill Rate Matters
It's a Customer Experience Metric
Customers don't care about your inventory management challenges. They care whether they get what they ordered. Fill rate directly measures that experience.
It Impacts Revenue
Unfilled orders often become lost sales. Customers go to competitors, cancel orders, or accept substitutes at lower price points. Each percentage point of fill rate has a revenue impact.
It Affects Relationships
For wholesale and retail channels, poor fill rate damages relationships. Retailers don't want to partner with brands that can't keep products in stock.
It Reveals Operational Health
Low fill rate is a symptom. The causes might be poor forecasting, inadequate safety stock, supplier issues, or demand spikes. Tracking fill rate helps you identify and fix root causes.
How to Calculate Fill Rate
There are several ways to calculate fill rate depending on what you want to measure:
Order Fill Rate
Percentage of orders shipped complete
Order Fill Rate = (Orders Shipped Complete / Total Orders) × 100
If you receive 500 orders and ship 450 complete (no partial shipments or backorders), your order fill rate is 90%.
Line Fill Rate
Percentage of order lines fulfilled
Line Fill Rate = (Lines Fulfilled / Total Lines) × 100
An order with 5 line items where 4 are shipped has an 80% line fill rate for that order.
Unit Fill Rate
Percentage of units fulfilled
Unit Fill Rate = (Units Shipped / Units Ordered) × 100
A customer orders 100 units, you ship 85. That's an 85% unit fill rate.
Which Should You Use?
Order fill rate is most customer-centric—it measures whether the customer got a complete order.
Unit fill rate gives more granular insight into inventory performance.
Most businesses track multiple fill rate metrics to get a complete picture.
Fill Rate Calculation Example
Let's say your business received these orders last month:
- Order A: 50 units ordered, 50 shipped, 3 lines, 3 complete
- Order B: 100 units ordered, 85 shipped, 5 lines, 4 complete
- Order C: 75 units ordered, 75 shipped, 2 lines, 2 complete
- Order D: 200 units ordered, 150 shipped, 4 lines, 3 complete
- Order E: 25 units ordered, 25 shipped, 1 line, 1 complete
Totals: 450 units ordered, 385 shipped, 15 lines, 13 complete
Unit Fill Rate: 385 / 450 = 85.5%
Line Fill Rate: 13 / 15 = 86.7%
Order Fill Rate: 3 orders complete out of 5 = 60%
Notice how order fill rate is lower—even one missing item makes the entire order "incomplete."
What's a Good Fill Rate?
Target fill rates vary by industry and channel:
- DTC / E-commerce: 95-98%
- Retail / Wholesale: 95-99%
- Amazon: 98%+ (or face penalties)
For Amazon specifically, fill rate directly impacts your account health and Buy Box eligibility. Falling below 95% can trigger warnings.
Fill Rate vs. Service Level
These terms are often confused:
Fill rate measures actual performance—what percentage of demand did you fulfill?
Service level is a target or goal—what percentage do you want to fulfill?
You set a service level target (e.g., 95%), and fill rate measures whether you're achieving it.
How to Improve Fill Rate
Better Forecasting
Most fill rate problems trace back to demand exceeding forecast. Improve forecast accuracy, and fill rate improves.
Appropriate Safety Stock
If you're frequently running out, your safety stock may be too lean. Increase buffers for important products.
Faster Replenishment
Shorter lead times mean you can respond faster when inventory runs low. Work with suppliers to reduce order-to-delivery time.
Demand Prioritization
When inventory is constrained, prioritize fulfillment to high-value customers or channels. Don't treat all orders equally when you can't fill them all.
Root Cause Analysis
Track why orders aren't filled completely. Is it the same few SKUs over and over? Supplier issues? Forecast misses? The fix depends on the cause.
Key Takeaways
- Fill rate measures what percentage of customer demand you fulfill from available inventory
- Order fill rate, line fill rate, and unit fill rate each tell a different story
- Target fill rates vary by channel: 95-98% is common for DTC, higher for retail and Amazon
- Fill rate is a customer experience metric—low fill rate means disappointed customers
- Improvement starts with understanding why you're not filling orders: forecasts, safety stock, suppliers, or demand spikes
Frequently Asked Questions
Q: What is fill rate?
Fill rate is the percentage of customer demand fulfilled from available stock. It measures how often you have products available when customers want to buy them.
Q: How do you calculate fill rate?
There are several methods. Unit fill rate = Units Shipped / Units Ordered × 100. Order fill rate = Orders Shipped Complete / Total Orders × 100. Each measures a different aspect of fulfillment performance.
Q: What's a good fill rate?
For most e-commerce and wholesale channels, 95-98% is a common target. Amazon requires 95%+ for account health. Your specific target depends on your industry and customer expectations.
Q: What's the difference between fill rate and service level?
Service level is your target—the percentage you aim to fulfill. Fill rate is your actual performance—what you achieved. You set a service level goal and measure fill rate to see if you hit it.
Q: How do I improve fill rate?
Common improvements include better forecasting, increased safety stock for key items, shorter lead times, and understanding root causes of stockouts.