ALB vs NLB cost: how to choose and estimate (LCU vs NLCU)

ALB vs NLB cost comparisons are easiest when you break the bill into two pieces: fixed hourly and capacity-unit usage (LCU for ALB, NLCU for NLB). The winner is usually driven by your traffic pattern: connections, bytes processed, and (for ALB) rule evaluations.

Quick decision guide

Cost is not the only decision factor, but it changes which drivers you need to measure. Use this table to decide what to model first.

Question Leaning ALB (L7) Leaning NLB (L4)
Do you need L7 routing features? Host/path-based routing, rules, HTTP features. Simple TCP/UDP forwarding, minimal L7 behavior.
What dominates your traffic? Moderate connections, many small HTTP requests. High connection rates or large byte throughput.
Biggest modeling risk Rule evaluations and peak request patterns. Peak connections/flows and bytes processed.

What to model

  • LB-hours (how many load balancers, how many hours/month)
  • Capacity units per hour (average and peak)
  • Bytes processed and connection patterns (often the biggest drivers)

Where to get the numbers

  • Requests: load balancer request count and average response size (for bytes processed).
  • Connections: active connections and new connections (peak and average matter).
  • Rules (ALB): if you rely on complex routing, validate whether rule evaluation volume is material for your traffic.

Practical tip: if you only have RPS and average payload size, estimate bytes processed as GB/month ≈ RPS × bytes/response × seconds/month ÷ 1e9, then validate against real metrics.

Step 1: estimate LCU/NLCU from metrics

ALB LCU / NLB NLCU calculator Estimate LCU from metrics

Step 2: estimate monthly cost

Once you have average units/hour, plug it into a cost calculator with your region pricing.

Load balancer cost calculator Load balancer cost guide

Example comparison (directional)

Use one representative hour (and one peak hour). For example:

  • Average: 250 RPS, 40 KB response → estimate bytes/hour and capacity units/hour.
  • Peak: 1,500 RPS for 2 hours/day → model peak separately because it can dominate capacity-unit charges.
  • Then add fixed hourly costs (LB-hours) for both options.

Common pitfalls

  • Ignoring peak hours (a small number of peak hours can dominate).
  • Using request count but forgetting payload size (bytes processed).
  • For ALB, forgetting rule evaluations for complex routing setups.

When ALB tends to win

  • You need L7 features and can consolidate behind fewer load balancers.
  • Traffic is many small requests with moderate connection rates.
  • Rule sets are simple (or rule evaluation driver is not dominant).

When NLB tends to win

  • You don’t need L7 features and want minimal processing overhead.
  • You have very high connection/flow patterns and simple forwarding.
  • Throughput/bytes processed is the main driver and you can measure it accurately.

Related tools

Data egress cost VPC transfer cost Cross-AZ transfer cost

Validation checklist

  • Validate the primary driver with measured usage from a representative window.
  • Confirm units and pricing units (per 10k vs per 1M, GB vs GiB) before trusting the estimate.
  • Re-check incident windows: retries/timeouts often multiply cost drivers.

Sources

  • AWS pricing overview: aws.amazon.com/pricing
  • Validate exact driver definitions and units in the official load balancer pricing docs for your region.

Related reading

Cost estimation checklist Network transfer costs Request-based pricing

Related guides

Estimate ALB LCU (and NLB NLCU) from metrics: quick methods
A practical guide to estimate ALB LCU and NLB NLCU from load balancer metrics: new connections, active connections, bytes processed, and rule evaluations — with a repeatable workflow and validation steps.
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FAQ

What’s the big cost difference between ALB and NLB?
Both usually have a fixed hourly fee plus capacity-unit billing, but ALB uses LCU drivers (including rule evaluations) while NLB uses NLCU-style drivers focused on connections and bytes processed.
When is ALB cheaper than NLB?
ALB can be cheaper when connection rates are moderate and you benefit from Layer 7 features without triggering high rule-evaluation or throughput drivers.
When is NLB cheaper than ALB?
NLB can be cheaper for high connection volume patterns and simpler Layer 4 forwarding, but you must still model bytes processed and peak connection behavior.
Last updated: 2026-01-27