An AWS Application Load Balancer (ALB) bill has two parts: a charge for the time the load balancer runs and a variable charge based on Load Balancer Capacity Units (LCUs). Bandwidth can drive the LCU charge, but it is only one of four usage dimensions. The highest normalized dimension for an hour determines the LCU usage—not whichever raw metric looks largest.
What an ALB LCU charge measures
AWS measures four dimensions of ALB activity: new connections, active connections, processed bytes, and rule evaluations. It converts each into LCU usage using the relevant thresholds, then charges for the highest dimension in the hour. This is why an ALB bill does not necessarily rise and fall with a bandwidth figure alone.
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For a standard ALB, AWS lists these thresholds per LCU:
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| Dimension | Threshold per LCU |
|---|---|
| New connections | 25 new connections per second |
| Active connections | 3,000 per minute, or 1,500 with mutual TLS |
| Processed bytes | 1 GB per hour for EC2 instances, containers, and IP targets; 0.4 GB per hour for Lambda targets |
| Rule evaluations | 1,000 per second |
AWS does not charge the first 10 processed rules in the rule-evaluation calculation. If 10 or fewer rules are configured, AWS says the rule-evaluations dimension is ignored. Mutual TLS and certificate key sizes can also affect applicable thresholds and calculations. See AWS’s ALB pricing details for the qualifications.
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Why bandwidth can mislead
Processed bytes are a real LCU dimension, and they can be the largest one. In AWS’s published illustration, processed bytes account for 1.08 LCUs, compared with 0.04 for new connections, 0.04 for active connections, and 0.25 for rule evaluations. That is an example, not a benchmark or a prediction for another workload.
Other traffic patterns can make a different dimension dominant. Many short-lived connections can increase new-connection usage; many simultaneous open connections can increase active-connection usage; and a request path involving many rule evaluations can raise that dimension. The bill is determined by the highest normalized usage, so raw bytes, connection counts, and rule counts cannot be compared directly.
How to find what is driving your bill
- Identify the load balancer and billing period. In AWS billing data,
LoadBalancerUsagerepresents running time andLCUUsagerepresents LCU usage. Reserved-capacity codes may appear when reservations apply. AWS explains these labels in its billing and usage report code guide. - Check the ALB’s CloudWatch metrics for the same period. Compare
ProcessedBytes,NewConnectionCount,ActiveConnectionCount, andRuleEvaluations. Also inspectConsumedLCUs, which AWS says is always reported. Metric definitions are in AWS’s ALB CloudWatch metrics documentation. - Normalize each dimension against its applicable threshold. Do not infer the leading dimension by comparing raw bytes with raw connection counts. Confirm whether targets are EC2 instances, containers, IPs, or Lambda, and account for mutual TLS and certificate key size where relevant.
- Estimate future cost with your own assumptions. Use the AWS Pricing Calculator with the actual Region and workload configuration. AWS’s pricing example uses US East (N. Virginia) rates and an assumed traffic profile; its figures should not be treated as universal or current for every Region.
Separate running-time cost from LCU cost
The runtime charge applies for each hour or partial hour that the ALB runs; the LCU charge reflects its measured usage. These are distinct billing components. AWS’s pricing page illustrates an hourly total of $0.03114 for a US East (N. Virginia) example, made up of a $0.0225 hourly charge and a $0.00864 LCU charge. Those are example rates on the page, not a general quote for another Region or configuration.
Without the billing report and corresponding CloudWatch metrics, it is not possible to say which dimension is responsible for a particular account’s charge. The billing codes show whether cost is runtime or usage; the four metrics and ConsumedLCUs help identify the usage pattern.
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