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Methodology & assumptions
1. System boundary
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Scope: This tool estimates energy, carbon and water for the
inference phase of GenAI models – the moment you generate text, images or video.
It does not include model training, embodied hardware impacts, or user devices.
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Equations:
IT energy (kWh) = (per-item Wh × count) / 1000
Facility energy (kWh) = IT energy × PUE (1.3)
CO₂e (kg) = Facility energy × grid intensity (0.4 kg CO₂e/kWh)
Water (L) = IT energy × WUE (1.0 L/kWh) + Facility energy × grid water factor (2.5 L/kWh)
2. Per-asset energy assumptions (IT energy)
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Images (~2.9 Wh per image): based on measurements for
Stable-Diffusion-class models (≈2.9 kWh for 1,000 images) on modern GPUs.
Applied to NanoBanana / Imagen 3, MidJourney, DALL·E 3 (ChatGPT) and Runway image generation.
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Video (clip-level, not frame-by-frame):
we assume that text-to-video models reuse computation across frames (temporal coherence,
shared latent representations) and do not re-run a full image model for every frame.
Using public benchmarks on H100-class hardware as a guide, we treat a short 720p clip as a
multiple of a still image, not frames × image cost:
- Runway / MidJourney video: ≈22 Wh per 5–6 s, 24 fps, 720p clip.
- Google Veo: ≈56 Wh per 8 s clip (larger, higher-quality model).
- Sora-style / very large models: ≈100 Wh per short clip (upper end of “central” range).
Earlier versions of this estimator used a simple “frames × still-image” model, which produced
much higher values; this clip-level approach is more realistic for modern video diffusion models.
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Text: calibrated to public estimates of around
4.3 g CO₂e per GPT-4-class request on a 0.4 kg CO₂e/kWh grid with PUE 1.3.
That corresponds to:
- Facility energy ≈ 0.0108 kWh per query.
- IT energy ≈ 0.0083 kWh per query = 8.3 Wh.
In the tool we use:
- ChatGPT / GPT-4, Gemini, Claude: 8.3 Wh per query.
- Llama / open models: 6.0 Wh per query (more efficient / smaller models).
So 100 GPT-4-class queries give ≈0.43 kg CO₂e and ≈3.5 L water.
3. Why training is not included
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Training a frontier model can require tens of MWh of electricity, but that cost is amortised
over billions of downstream inferences. The per-asset share is uncertain and speculative.
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To keep this tool usable at project level, we focus on the marginal footprint of
generating each asset, which teams can actually influence through volume, media mix and asset reuse.
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Training impacts can be discussed separately (e.g. “this model required ≈X MWh to train”),
but they are not allocated per asset in this estimator.
4. Impact of building this calculator
Developing and iterating this estimator involved a few hundred ChatGPT-style requests.
Using the same text assumptions (~8.3 Wh IT, ~0.0108 kWh facility per query), a design process
with 300 prompts would use roughly:
- Facility energy: ≈3.2 kWh
- CO₂e: ≈1.3 kg CO₂e
- Water: ≈10–12 L (combining data-centre cooling and grid water)
That is equivalent to only a few tens of kilometres of driving in a petrol car and a fraction of a
standard shower. It is small compared to a GenAI-heavy campaign, but we note it here for transparency.
This “tool-building” footprint is not added to project calculations.
5. Real-world analogies
- Driving: ≈0.192 kg CO₂e per km for an average petrol car.
- Showers: ≈80 L of water per standard 8-minute shower.
- Trees: ≈25 kg CO₂e sequestered per mature tree per year.
- Glasses of water: 250 ml per glass.
All numbers are indicative. The tool is designed for comparison, estimation and storytelling – not
formal carbon accounting or supplier-specific reporting.