UsesLevel 2 of 6 machine operationMachine operation, level 2 of 6Used to calculate 1 entry, level 4Calculated with 2 entries, levels 1 and 2Database structure 
6Territories
5Organisations
4Occupations and activities
3Uses
1Calculation factorsSynthesise one minute of voice
The server electricity used to make an AI speak for a minute. Projet Celsius estimate.
- The calculation covers the model writing the audio tokens.
- 100% of the calculation rests on database assumptions; it does not measure actual use.
- Out of scope: data centre cooling, server manufacturing and the conversion of tokens into sound.
Sentence to citeSynthesise a minute of voice, Projet Celsius estimate: 0.53 gCO2e per minute of voice, for 1.2 Wh of electricity, servers worldwide (458 gCO2e/kWh).
- Calculated with
- Used to calculate
How the calculation is built
No measurement is published: the database counts the 1,200 audio tokens that OpenAI bills for a minute of voice, at the cost of a written token.
Comparison with the other machine operations
Characteristics
| Unit | 1 minute of voice |
|---|---|
| Default location | world, 458 gCO2e/kWh (Ember 2025, life cycle); 11 other locations to choose from |
| Counted | the model writing the audio tokens |
| Not counted | data centre cooling, server manufacturing and the conversion of tokens into sound |
| Status | estimated |
All the characteristics
| Identifier | IA-0019, projetcelsius.com/en/ai/database/IA-0019/ |
|---|---|
| Version | 0.1 of 2 November 2026 |
| Category | Machine operations, what the server computes |
| Choice of the selected value | database calculation from the entries this one is made of, at the quantities of the unit |
| Sources | calculation of the database |
| Licence | CC BY 4.0 |
Usage parameters
Advanced settings
Result for the chosen case
Breakdown by item
Quantity, unit value, contribution and nature of the data for each item
| Item | Quantity | Unit value | Contribution | Share | Nature of the data |
|---|---|---|---|---|---|
| Write 1,000 tokens | × 1.2 | 0.96 Wh | 1.2 Wh | 100 % | assumption |
Entries that use it (1)
Sources of the calculation
3 publications, for this entry and those used to calculate it, with the chosen parameters.
The result is calculated by Projet Celsius. The sources below support its uses, its factors and its conversion; they do not all measure this total.
Uses and assumptions
These publications shed light on AI tasks and uses. They do not measure the carbon footprint of the case calculated.
Role and limits : OpenAI
What the publication covers. audio tokens: one per 100 milliseconds of the user's speech, one per 50 milliseconds of the assistant's speech
What it does not cover. electricity
Reading by the database. The publisher's billing rule, read in the page excerpt
Synthesise a minute → : Write 1,000 tokens →
The 1,200 audio tokens of one minute of voice, at the cost of a written token: no published measurement
Scope of the figure used. server, excluding the data centre
Limit. The quantity and the share entrusted to AI are database assumptions, not a measured footprint.
Synthesise a minute → : Write 1,000 tokens →
Length convention: one minute of voice spoken by an AI
Scope of the figure used. One audio token per 50 milliseconds of the assistant's speech at OpenAI
Limit. This publication supports the quantity of text or content processed, not its carbon footprint.
Energy and factors
The references of the selected values and of the entries used in this calculation.
Watershed · Aug. 2026
Estimating GHG Emissions from AI Use: Framework for Corporate-Level Measurement ↗ (new tab)
Role and limits : Watershed
Author. Bistline, Ulissi, Davis, Glidden, Joyce, Li, Mohsenin and Suh (Watershed)
What the publication covers. factors per 1,000 tokens read and written at the server before PUE (host and standby machines included), PUE separate (1.10 for a large operator, 1.56 for an unknown operator)
What it does not cover. clean measurements, the model and the hardware
Reading by the database. Default factors proposed for review (public data as of June 2026); for a large operator, taken from Google's measurement published in 2025 (Elsworth et al.), which already contains the data centre overhead; constant per token, they underestimate long contexts and agents according to the authors
Reference for the variant "Medium model, Watershed default factor"
Scope of the figure used. Default factor for 1,000 tokens written, medium model, large operator, at the server before PUE (Watershed table 2, public data as of June 2026)
Limit. 3 times the reading factor, based on the ratio between writing and reading selected by Watershed (Patel et al., Splitwise, 2024). Same derivation and same caveat as for reading: Google's 0.24 Wh already include about 8% of data centre. Values proposed for review, final at the next version of the framework
Conversion into carbon
The source of the electricity factor of the selected location.
Worldwide: 458 gCO2e/kWh, life cycle.
Role and limits : Ember
Author. Ember, Our World in Data
What the publication covers. electricity generation over the life cycle, by country
What it does not cover. guarantees of origin
Reading by the database. The same source for all countries
Conversion of electricity into carbon: worldwide
Scope of the figure used. the production of electricity over the life cycle, including power plant construction and fuels
Limit. An average for the chosen country, not the electricity contract or the data centre of a specific service.
Nature of the data
Published readings, conventions, assumptions
- Projet Celsius assumptions 100 %
Calculation assumptions
Quantities, nature and source of each assumption
Write 1,000 tokens : × 1.2
The 1,200 audio tokens of one minute of voice, at the cost of a written token: no published measurement
Methodology conventions
With their alternatives
| The default location | Without other information, the servers are in the world, at the world average electricity |
|---|---|
| Electricity, location-based, on a life cycle basis | The kilowatt-hour is that of the servers' country, on a life cycle basis, from a single source for all countries |
| Two significant figures | A calculated value is rounded to two significant figures, a published value is reproduced with the precision of its source; the calculation keeps full precision |
| The formula | the sum of what makes up the entry, then CO2e: electricity (Wh) multiplied by the carbon intensity of the server location (gCO2e/kWh), divided by 1,000 |
| Calculate a case without an entry | The formula, the default values and a step-by-step example |
History
Entry in version 0.1 of 2 November 2026, in the database in version 0.4
- 2 November 2026Version 0.1 of the entry, as of the date of its current value.
- 31 October 2026Creation of the database, in its first version (0.1).
