# What is per-second billing?

Per-second billing charges for cloud resources by the second they run, instead of rounding every start up to a whole hour or minute.

**Runtime bills compute with no one-minute minimum, and bills CPU by the work
it measures: $0.025 per active vCPU-hour, which is a CPU-second at a
3,600th of that.** Memory is billed while the sandbox runs, at $0.0075
per GiB-hour, and a pause stops compute billing at once
([pricing](/docs/pricing)).

## A short history

Clouds billed virtual machines by the hour until 2 October 2017, when Amazon
announced that EC2 Linux instances "will be billed on one second increments,
with a minimum of 60 seconds". Other clouds followed. Functions went further:
AWS Lambda bills duration by the millisecond.

## What the unit hides

The unit is only half the bill. The other half is what is counted in each
second:

| Billing                       | A one-minute run, 2 vCPUs, busy for 10 seconds |
| ----------------------------- | ---------------------------------------------- |
| Per hour, allocated vCPUs     | A full hour of 2 vCPUs                         |
| Per second, 60-second minimum | 60 seconds of 2 vCPUs                          |
| Per second, allocated vCPUs   | 60 seconds of 2 vCPUs                          |
| Per second, measured CPU      | 20 CPU-seconds, plus memory for 60 seconds     |

Rounding matters for short runs too. A provider that rounds each run up to the
minute bills a ten-second check as sixty; CodeSandbox does, and on 40-second
runs that makes the example job $2.48 there
against $0.47 on Runtime
([CodeSandbox vs AWS Lambda MicroVMs](/compare/codesandbox-vs-aws-lambda-microvms)).

## Worked on Runtime

1,000 runs of a 2 vCPU, 4 GiB sandbox, 60 seconds each, with 20 CPU-seconds of
work per run:

```text
CPU:     1,000 × 20 s / 3,600 × $0.025      = $0.14
Memory:  1,000 × 60 s / 3,600 × 4 GiB × $0.0075 = $0.50
Total:                                          $0.64
```

## Related

- [What is serverless computing?](/glossary/serverless-computing)
- [What is a CPU floor?](/glossary/cpu-floor)
- [What is a spending limit?](/glossary/spending-limit)
- [Sandbox cost calculator](/calculators/sandbox-cost-calculator)

## Sources

Checked 27 September 2026.

- [Announcing Amazon EC2 per-second billing, AWS](https://aws.amazon.com/about-aws/whats-new/2017/10/announcing-amazon-ec2-per-second-billing/)
- [AWS Lambda pricing](https://aws.amazon.com/lambda/pricing/)
- [Runtime pricing](/docs/pricing)