ALB LCU cost explained: how load balancer capacity units bill you

Quick answer

An Application Load Balancer bills about $0.0225 per hour (roughly $16.20 per month) plus a Load Balancer Capacity Unit (LCU) charge of about $0.008 per LCU-hour. One LCU covers four dimensions measured per hour: 25 new connections per second, 3,000 active connections per minute, 1 GB of processed bytes per hour, and 1,000 rule evaluations per second. You are billed on the highest of the four, not the sum. So a data-heavy app is billed on processed bytes, while a high-connection app is billed on connections. The lesson: find which dimension dominates your LCU bill, because that is the one to optimize.

The Application Load Balancer has a two-part price: a modest hourly fee and a usage-based charge measured in Load Balancer Capacity Units. The hourly fee is easy to understand. The LCU is where the real cost lives and where most confusion starts, because it measures four different things and bills you on whichever is highest.

The two components

Component	Rate
Hourly fee	~$0.0225/hr (~$16.20/mo)
LCU fee	~$0.008 per LCU-hour

Every ALB costs the hourly fee just for existing, about $16.20 a month. On top of that, you pay for the LCUs your traffic consumes at about $0.008 each per hour. The trick is understanding what an LCU represents.

The four LCU dimensions

Dimension	One LCU equals
New connections	25 per second
Active connections	3,000 per minute
Processed bytes	1 GB per hour
Rule evaluations	1,000 per second

For each hour, the ALB measures all four dimensions, converts each to an LCU count, and bills you on the single highest one, not the sum. This matters enormously. An application serving large downloads is dominated by processed bytes: 100 GB in an hour is 100 LCUs on that dimension alone. A high-traffic API with many short requests is dominated by new connections. A microservice with hundreds of routing rules can be dominated by rule evaluations.

Working an example

Suppose an ALB processes 50 GB per hour (50 LCUs of processed bytes), handles 10 new connections per second (0.4 LCUs), 6,000 active connections per minute (2 LCUs), and 500 rule evaluations per second (0.5 LCUs). The bill is on 50 LCUs, the processed-bytes dimension, at about $0.008 each, roughly $0.40 per hour or $290 a month, plus the base fee. Every other dimension is irrelevant to the bill because processed bytes dominates. To cut this ALB's cost, you reduce bytes, not connections.

Keeping LCUs down

First, identify your dominant dimension in CloudWatch by comparing the LCU metrics. If processed bytes dominate, compress responses, offload large downloads to CloudFront or S3 so they bypass the ALB, and cache aggressively. If new connections dominate, use keep-alive so clients reuse connections instead of opening new ones. If rule evaluations dominate, simplify listener rules. Consolidating many small services behind one ALB rather than running an ALB per service also saves the base fee, the sameALB versus NLB economics that make the load balancer choice a cost decision. For pure TCP pass-through, an NLB with its cheaper capacity units may cost less.

Because the LCU bill depends on which dimension dominates, the optimization is specific to your traffic shape. Price your load balancer against the resource catalog so the LCU cost is estimated from real traffic before the ALB goes live.

FAQ

What is an LCU on an Application Load Balancer?

A Load Balancer Capacity Unit is the usage-based billing unit for an ALB, costing about $0.008 per LCU-hour on top of the roughly $0.0225 per hour base fee. One LCU covers four dimensions: 25 new connections per second, 3,000 active connections per minute, 1 GB of processed bytes per hour, and 1,000 rule evaluations per second. You are billed on the highest of the four each hour.

How is the ALB LCU charge calculated?

Each hour, the ALB measures all four dimensions (new connections, active connections, processed bytes, and rule evaluations), converts each to an LCU count, and bills you on the single highest one, not the sum. So a data-heavy app is billed on processed bytes while a high-connection app is billed on connections. Identifying the dominant dimension tells you what to optimize.

Why is my ALB more expensive than the hourly fee suggests?

Because the LCU charge on top of the base fee can be large for high-traffic workloads. An ALB processing 50 GB per hour is billed on 50 LCUs of processed bytes, roughly $0.40 an hour or $290 a month, far more than the $16.20 base. The hourly fee is just the floor; the LCU charge based on your dominant traffic dimension is usually the bigger part.

How do I reduce ALB LCU cost?

Identify your dominant dimension in CloudWatch first. If processed bytes dominate, compress responses, offload large downloads to CloudFront or S3 so they bypass the ALB, and cache aggressively. If new connections dominate, use keep-alive so clients reuse connections. If rule evaluations dominate, simplify listener rules. Consolidating services behind one ALB also saves the base fee.

Is an NLB cheaper than an ALB?

It can be for the right workload. An NLB uses Network Load Balancer Capacity Units at about $0.006 each, cheaper than the ALB's $0.008 LCU, and handles TCP pass-through efficiently without the ALB's layer-7 features. For simple TCP traffic an NLB may cost less, while an ALB is worth its higher LCU rate when you need HTTP routing, host and path rules, and other layer-7 capabilities.

How does C3X help with ALB cost?

C3X prices your Application Load Balancer from Terraform before you deploy, including the base fee, so the load balancer cost is visible in the pull request. Combined with your expected traffic shape, that helps you anticipate which LCU dimension will dominate and whether consolidating services or choosing an NLB would cost less, at design time rather than after the LCU charges appear on the bill.

What to do next

Understand your load balancer cost before you deploy. C3X reads your Terraform and prices your resources against a live catalog. Start with the quickstart.