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Azure Cosmos DB RU Calculator

Convert reads, writes and queries into Cosmos DB request units and price provisioned, autoscale and multi-region throughput.

About Azure Cosmos DB RU Calculator

Cosmos DB normalises every operation into request units: a 1 KB point read is 1 RU, a 1 KB write about 5 RU because of index maintenance, and queries are whatever the request-charge header reports. Autoscale bills 1.5× the standard rate but only for the RU/s actually used between 10% and 100% of your maximum, so it wins when the peak-to-average ratio is worse than about 1.5. Provisioned throughput is billed per region every hour whether you use it or not, so an over-provisioned container replicated to three regions with multi-region writes costs six times what the numbers suggest — verify the per-100-RU/s rate for your region and API in the Azure pricing calculator.

Formula

Azure Cosmos DB RU

RU/s = reads × (1 RU per KB) + writes × (5 RU per KB) + queries × RU per query, rounded up to the next 100; cost = RU/s ÷ 100 × rate × 730 × regions, ×1.5 on autoscale and ×2 with multi-region writes.

RU
Request unit — the normalised cost of one database operation
autoscale floor
Autoscale never bills below 10% of the maximum RU/s you set
region factor
Provisioned throughput is billed in full in every region you replicate to

Worked example

With the default values below, Azure Cosmos DB RU Calculator returns Monthly Cost of $580.52. Change any input above and every figure here is recalculated in your browser.

Inputs used

Point reads per secondaccepts 0–10,000,000 reads/s
800 reads/s
Writes per secondaccepts 0–10,000,000 writes/s
150 writes/s
Average item sizeaccepts 1–2,048 KB
2 KB
Queries per secondaccepts 0–1,000,000 queries/s
60 queries/s
RU per queryaccepts 1–10,000 RU
12 RU
Throughput modeone of Standard provisioned, Autoscale (1.5× rate, floor at 10% of max)
Standard provisioned
Average autoscale utilisationaccepts 10–100 %
35 %
Regionsaccepts 1–30 regions
2 regions
Multi-region writes enabled
No
Price per 100 RU/saccepts 0–1 USD/hour
0.008 USD/hour
Transactional storageaccepts 0–1,000,000 GB
250 GB
Storage price per GBaccepts 0–10 USD/GB-month
0.25 USD/GB-month

Results

Monthly Cost
$580.52
Required Throughput
3,900 RU/s
Billed Throughput
3,900 RU/s
Throughput Charge
$455.52
Storage Charge
$125.00
RU per Write
10.0 RU

Step by step

  1. 1Values used
  2. 2Azure Cosmos DB RU
  3. 3Monthly Cost= 580.52
  4. 4Required Throughput= 3,900 RU/s
  5. 5Billed Throughput= 3,900 RU/s
  6. 6Throughput Charge= 455.52
  7. 7Storage Charge= 125.00
  8. 8RU per Write= 10.0 RU

Assumptions and limits

  • The result is derived only from the 12 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Azure Cosmos DB RU calculated?

RU/s = reads × (1 RU per KB) + writes × (5 RU per KB) + queries × RU per query, rounded up to the next 100; cost = RU/s ÷ 100 × rate × 730 × regions, ×1.5 on autoscale and ×2 with multi-region writes. Cosmos DB normalises every operation into request units: a 1 KB point read is 1 RU, a 1 KB write about 5 RU because of index maintenance, and queries are whatever the request-charge header reports. Autoscale bills 1.5× the standard rate but only for the RU/s actually used between 10% and 100% of your maximum, so it wins when the peak-to-average ratio is worse than about 1.5.

Why does Azure Cosmos DB RU matter?

Provisioned throughput is billed per region every hour whether you use it or not, so an over-provisioned container replicated to three regions with multi-region writes costs six times what the numbers suggest — verify the per-100-RU/s rate for your region and API in the Azure pricing calculator.

What values do I need to enter?

This calculator takes 12 inputs: Point reads per second, Writes per second, Average item size, Queries per second, RU per query, Throughput mode, Average autoscale utilisation, Regions, Multi-region writes enabled, Price per 100 RU/s, Transactional storage, Storage price per GB. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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