Using the Values and Counts method enables you to publish up to 150 values per metric with one PutMetricData request, and supports retrieving percentile statistics on this data.

Each PutMetricData request is limited to 40 KB in size for HTTP POST requests. You can send a payload compressed by gzip. Each request is also limited to no more than 20 different metrics.

aws cloudwatch put-metric-data --namespace "Usage Metrics" --metric-data file://metric.json

The values for the metric itself are stored in the JSON file, metric.json.

Here are the contents of that file:

[
  {
    "MetricName": "New Posts",
    "Timestamp": "Wednesday, June 12, 2013 8:28:20 PM",
    "Value": 0.50,
    "Unit": "Count"
  }
]

CloudWatch API PutMetricData