google_pubsub_subscription cost estimation

A google_pubsub_subscription attaches a consumer to a Pub/Sub topic, in pull or push form, and controls acknowledgment deadlines, retention, dead-letter policy, and ordering. Creating the subscription is free. Pub/Sub does not charge for having a subscription; it charges for the message data that moves through and is stored by it.

Throughput is the primary cost, billed per TiB of message data, and it is counted on both the publish side (into the topic) and the delivery side (out to each subscription). This matters: fan-out multiplies delivery. A topic with three subscriptions delivers each message three times, so three subscriptions on the same topic roughly triple the delivery throughput cost. The subscription is where that multiplication happens.

Two more cost drivers live on the subscription. Retained acknowledged messages and seek/replay retention are billed per GB-month of storage, so long retention windows on a high-volume subscription add up. And a push subscription to an endpoint in another region, or a subscriber that pulls across regions, incurs egress. c3x prices the delivery throughput, retained storage, and egress a subscription drives and links it to the topic it consumes.

Terraform example

A minimal but realistic configuration that C3X can estimate.

resource "google_pubsub_subscription" "worker" { name = "worker-sub" topic = google_pubsub_topic.events.id ack_deadline_seconds = 20 message_retention_duration = "86400s" retain_acked_messages = false expiration_policy { ttl = "" } }

Pricing dimensions

What you actually pay for when you provision google_pubsub_subscription.

Dimension	Unit	What's being charged
Subscription	free	Creating and holding a subscription has no charge. Cost is on the data that flows through it. $0
Delivery throughput	per TiB	Message data delivered to the subscription, counted per subscription so fan-out multiplies it. ~$40/TiB delivered
Retained message storage	per GB-month	Storage for unacked messages, retained acked messages, and seek/replay retention windows. ~$0.27/GB-month
Egress to subscriber	per GB	Cross-region or internet egress when a push endpoint or puller is in another region.

Optimization tips

Common ways to reduce google_pubsub_subscription cost without changing the workload.

Avoid unnecessary fan-out

Cuts duplicated delivery throughput

Each subscription on a topic is billed for its own delivery throughput. Consolidating consumers that can share a subscription avoids paying to deliver the same messages multiple times.

Keep retention windows tight

Less retained-storage cost

Long message_retention_duration and retain_acked_messages hold data as billed storage. Set retention to the minimum replay window your consumers actually need.

Keep subscribers in the topic's region

A push endpoint or puller in another region adds egress on every message. Colocating the subscriber with the topic avoids cross-region transfer charges.

FAQ

Does a Pub/Sub subscription cost money?

Not to exist. Cost comes from message throughput delivered to it (per TiB), storage for retained or unacked messages (per GB-month), and egress if the subscriber is in another region.

Why do more subscriptions increase my Pub/Sub bill?

Throughput is counted per subscription on delivery. A topic with three subscriptions delivers each message three times, so fan-out multiplies the delivery throughput cost.

How do I estimate subscription cost?

Estimate messages delivered per month in TiB, the retained storage in GB, and any cross-region egress. c3x prices delivery throughput, retention, and egress and links the subscription to its topic.

`google_pubsub_subscription` cost estimation