CloudWatch Metric Guide
NumberOfObjectsAmazon S3 CloudWatch metric
NumberOfObjects reports the total count of objects in a general purpose bucket across all storage classes — including current and noncurrent versions, delete markers, and the parts of incomplete multipart uploads. Like BucketSizeBytes, it is a free storage metric published once per day, filtered with StorageType=AllStorageTypes.
What it measures
About NumberOfObjects
NumberOfObjects reports the total count of objects in a general purpose bucket across all storage classes — including current and noncurrent versions, delete markers, and the parts of incomplete multipart uploads. Like BucketSizeBytes, it is a free storage metric published once per day, filtered with StorageType=AllStorageTypes.
| Namespace | AWS/S3 |
| Metric name | NumberOfObjects |
| Unit | Count |
| AWS docs | Official Amazon S3 metrics reference |
Why this metric matters
NumberOfObjects tells a different story than BucketSizeBytes. A bucket can have a stable total size while its object count explodes — millions of tiny objects driven by high-frequency writes (per-event logging, IoT ingestion, thumbnail generation) — which disproportionately inflates PUT/LIST/GET request costs and makes lifecycle rules and inventory jobs far slower to run.
In versioned buckets, NumberOfObjects also includes delete markers and noncurrent versions. A count that keeps climbing while your application's visible object list stays flat is a strong signal that deletions are only creating delete markers — the underlying data (and its storage cost) is still there.
Recommended alarm threshold for NumberOfObjects
Recommended threshold
Alarm on a >20% day-over-day increase (or use CloudWatch Anomaly Detection) rather than an absolute count
As with BucketSizeBytes, AWS does not publish a universal object-count threshold since normal counts vary by orders of magnitude between buckets. A day-over-day percentage threshold (Nuberio recommendation) catches an object-count explosion — a stuck cleanup job, a versioning misconfiguration, or a write-amplification bug — while adapting automatically as legitimate usage grows.
Is your NumberOfObjects alarm already set up correctly?
The free Nuberio Audit scans your CloudWatch setup and flags missing or misconfigured alarms — including NumberOfObjects — in 5 minutes.
Common failures that show up in NumberOfObjects
When NumberOfObjects reaches an alarm threshold, these are the most common root causes — in order of how often Nuberio sees them across customer AWS accounts.
High-frequency small-object writes (IoT ingestion, per-request logging) creating millions of objects disproportionate to actual data volume
Versioning enabled without a lifecycle expiration rule, so delete markers and noncurrent versions accumulate indefinitely
A scheduled cleanup, archival, or deduplication job that silently stopped running
Incomplete multipart uploads counted as parts after a large-file upload workflow started failing repeatedly
A migration, backup, or fan-out job duplicating objects across prefixes
How the Nuberio Audit checks NumberOfObjects
The free Audit scans every Amazon S3 resource in your account and checks whether a NumberOfObjects alarm exists, whether its threshold and evaluation period are configured sensibly, and flags it if it's missing entirely. Every finding comes with the exact CLI command to fix it — read-only access, no credit card, results in about 5 minutes.
Nuberio Audit
Scans your CloudWatch setup for missing or misconfigured NumberOfObjects alarms. Free, 5-minute read-only scan.
Related Amazon S3 metrics
NumberOfObjects rarely fails in isolation. These metrics tend to correlate — monitor them together for complete Amazon S3 coverage.
FAQ
Frequently asked questions about NumberOfObjects
Common questions about setting up CloudWatch alarms for NumberOfObjects in Amazon S3.
What is the recommended CloudWatch alarm threshold for NumberOfObjects?+
Alarm on a >20% day-over-day increase (or use CloudWatch Anomaly Detection) rather than an absolute count. As with BucketSizeBytes, AWS does not publish a universal object-count threshold since normal counts vary by orders of magnitude between buckets. A day-over-day percentage threshold (Nuberio recommendation) catches an object-count explosion — a stuck cleanup job, a versioning misconfiguration, or a write-amplification bug — while adapting automatically as legitimate usage grows.
Which CloudWatch namespace does NumberOfObjects belong to?+
NumberOfObjects is published in the AWS/S3 namespace with a unit of Count. You can find it in the CloudWatch console under "Metrics" → "AWS/S3". See the Amazon S3 CloudWatch metrics reference in the AWS documentation.
Does Nuberio automatically create CloudWatch alarms for NumberOfObjects?+
No — the free Nuberio Audit does not create alarms for you. It scans your CloudWatch setup and tells you which Amazon S3 resources are missing a NumberOfObjects alarm, then gives you the exact CLI command to create it yourself.
Can I use Nuberio without already having a NumberOfObjects alarm set up?+
Yes. The free Audit works whether or not you have any NumberOfObjects alarm configured — it reads the resource directly from CloudWatch and tells you which resources need one, plus the copy-paste AWS CLI command to create it.
This page is part of the CloudWatch metric guide — thresholds and debugging guidance for every metric across RDS, Lambda, ECS, ALB, EC2, and DynamoDB. To find which Amazon S3 alarms your account is missing — including NumberOfObjects — run the free CloudWatch alarm audit. The scan takes under 5 minutes and requires no account.