The Carbon Footprint of Email Signatures

(An illustrative calculation of how much additional CO₂-equivalent is caused solely by the use of email signatures.)

How many emails actually carry a signature?

| Step | Figure | Source | Comment | |——|——–|——–|———| | Global emails sent/received per day (2025) | 376.4 billion | Statista via EmailToolTester | — | | Share filtered as spam (2023-24 average) | 46 % | Cisco Talos Intelligence | ≈ 160 bn spam mails/day | | Legitimate messages | 203 billion/day | Calculation | 376.4 bn × (1 – 0.46) | | Users who add a signature to at least one account | ~90 % | HubSpot survey | — | | Estimated share of legitimate mail that carries a designed signature | 60 % | Assumption (business-mail ratios) | — |

Result → ≈ 122 billion emails per day arrive with an appended signature.

How big is a typical signature?

| Type of signature | Typical weight* | |——————-|—————–| | Lean – text + compressed logo | ≈ 22 kB | | Rich – logo + head-shot + banner | ≈ 80 kB |

*On-disk sizes. Base-64 encoding during transmission adds ~33 %, but we keep the conservative raw sizes.

CO₂-equivalent per unit of data transferred & stored

| Emissions factor | Derivation | Comment | |——————|————|———| | High-legacy: 15 g CO₂e / MB | ADEME & The Shift Project | Includes device manufacture + older, dirtier grid | | Current-best: 80 g CO₂e / GB (0.08 g / MB) | 0.194 kWh / GB (IEA) × 436 g CO₂ / kWh (2024 grid mix) | Reflects 2024 efficiencies & cleaner grid |

Using both factors shows today’s likely range.

Daily and annual signature emissions (2025)

Data volume

Signature-e-mails per day   = 122 bn
Extra bytes per e-mail      = 22–80 kB
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Net extra data per day      = 2.6–9.3 PB

(1 PB ≈ 1 048 576 GB)

Convert to CO₂e

| Scenario | g CO₂e / email | t CO₂e / day | Mt CO₂e / year | |———-|—————|——————|——————–| | Low – lean sig + current factor | 0.002 g | 0.23 t | 0.08 Mt | | Moderate – lean sig + high factor | 0.4 g | 49 t | 18 Mt | | High – rich sig + high factor | 1.2 g | 146 t | 53 Mt |

What does that mean?

  • Even with present-day efficiencies, the marketing-signature “tax” plausibly adds 20–50 million tonnes CO₂e each year – comparable to the annual emissions of Switzerland or New Zealand.
  • If you apply the most up-to-date energy-intensity numbers, the footprint collapses to < 0.1 Mt; many corporate carbon calculators still default to the higher factors.

Per-person perspective

For an office worker who sends 40 emails/day:

If their signature is… Extra CO₂e each year
Lean (22 kB) & modern grid factor ≈ 3 g (negligible)
Lean but using older factor ≈ 4 kg
Rich (80 kB) & older factor ≈ 12 kg

Removing a heavy signature is therefore about the same annual benefit as driving ~50 km less in a small petrol car.

Key uncertainties & how to improve the estimate

  1. Energy-intensity of data traffic keeps falling ~50 % every two years; pick factors that match your region and year.
  2. Grid carbon intensity varies five-fold between regions; hosting on 100 % renewables slashes emissions further.
  3. Behavioural patterns (reply chains, clients that strip images, local caching) can lower the bytes actually travelling.
  4. Storage vs. transmission – this calculation treats storage as negligible; if every copy is retained for years in high-availability storage, add ≈ 0.1 kWh per GB per year.