Starlight Tools

Email Carbon Footprint Calculator: Estimate CO₂e from Emails and Attachments

Email Carbon Footprint Calculator: Estimate CO₂e from Emails and Attachments. Email emissions vary widely by device, message length, attachment size, recipients, storage time, and grid mix, so treat the result as a transparent estimate rather than an audit.

How much CO₂ does an email produce?

A single email can range from a tiny fraction of a gram to tens of grams of CO₂e. The Carbon Literacy Project cites these benchmark examples, based on Mike Berners-Lee's email estimates:

0.03 gspam filtered before inbox
0.2 gshort email on a phone
0.3 gshort email on a laptop
17 glong email on a laptop
26 ghigh-effort email blast

Source: The Carbon Literacy Project, "The carbon cost of an email".

Calculate Your Email CO₂e

emails
people
min
MB
years
g
g
Benchmark mode is useful for fast ballparks; detailed mode separates transfer, storage, reading, attachment, and recipient effects.
Runs locally in your browser.

Example scenarios

Results

Total footprint – kg CO₂e
Email volume –
Per email – g CO₂e
Assumes —.
Tip: switch scenarios or detailed mode to see how file size, recipients, and storage time change things.
Sending / transfer CO₂e—
Storage CO₂e—
Reading / device CO₂e—
Attachments CO₂e—
Copies / recipients CO₂e—
  • Kettles boiled: —
  • Car km driven: —
  • Tree-months (1 tree ≈ 22 kg/yr): —
  • Elephants: —

Assumptions and sources

Defaults are adjustable because email emissions are not a fixed physical constant. The table shows what each baseline means and why it was chosen.

Default What it means Why this value Source / date
4 g CO₂e per text email Benchmark factor for a typical text-only email in quick estimates. A middle-ground ballpark between very short modern email examples and older higher estimates. Mike Berners-Lee estimates as summarized by Carbon Literacy Project; reviewed 10 June 2026.
50 g CO₂e per attachment email Benchmark factor for an email with a meaningful attachment. Kept as a conservative quick-estimate default because large files and multiple recipients can dominate. Mike Berners-Lee / Carbon Literacy discussion of email footprint ranges; reviewed 10 June 2026.
75 KB average message size Detailed-model body size before attachments. Represents a compact HTML/text email with headers and formatting, not a media-heavy newsletter. Starlight Tools modelling default; reviewed 10 June 2026.
0.06 kWh per GB transferred Electricity used to move data through networks. Modern network energy intensity is much lower than early internet estimates, but varies by network and year. Recent data-energy reporting and IEA-style network intensity ranges; reviewed 10 June 2026.
0.5 kWh per GB per year stored Electricity to keep email data available in data centres for a year. A practical, adjustable default that makes retention time visible without claiming provider-specific precision. Data-centre storage modelling default; reviewed 10 June 2026.
300 g CO₂e per kWh Grid carbon intensity used by the detailed model. A broad default between cleaner and more fossil-heavy grids; change it for your region if known. General grid-intensity reporting; reviewed 10 June 2026.
Email volume context Why small per-email estimates still matter at scale. Global email volumes are very large, so mailing list hygiene and unnecessary recipients can add up. Statista-style email volume reporting; reviewed 10 June 2026.

Methodology

Benchmark mode uses per-email CO₂e factors for text-only and attachment emails. Detailed mode estimates data transfer, storage duration, grid carbon intensity, device reading energy, and duplicate copies from recipients and backups.

Formula summary

# Benchmark mode
total_CO2e_g = sent_emails × recipients × [(1 - attachment_share) × text_email_g
              + attachment_share × attachment_email_g]

# Detailed mode
text_GB       = sent_emails × text_KB / 1024 / 1024
attachment_GB = sent_emails × attachment_share × attachment_MB / 1024
delivered_GB  = (text_GB + attachment_GB) × recipients
transfer_g    = delivered_GB × network_kWh_per_GB × grid_gCO2e_per_kWh
storage_g     = delivered_GB × backup_factor × storage_kWh_per_GB_year × years_stored × grid_gCO2e_per_kWh
reading_g     = sent_emails × recipients × read_minutes × device_Wh_per_min / 1000 × grid_gCO2e_per_kWh
total_CO2e_g  = transfer_g + storage_g + reading_g
sent_emails
The number of emails you are modelling. In daily/yearly mode, this is emails per day multiplied by days per year.
attachment_share
The share of emails with attachments, expressed from 0 to 1. For one-email mode, any attachment size above 0 counts as attached.
recipients
Recipient copies multiply transfer, storage, and reading energy because each person receives and may open a copy.
grid_gCO2e_per_kWh
The carbon intensity of electricity. Lower-carbon grids reduce operational CO₂e for the same email activity.

Worked example

If you send 40 emails per workday for 250 days, with 15% attachments, 2 recipients, 0.5 minutes of reading time, 3 MB average attachments, and one year of storage, detailed mode first converts the email data to GB, multiplies it by recipients and backup copies, then applies network, storage, device, and grid assumptions to produce the total.

What actually reduces email emissions?

  • Reduce unnecessary recipients: CC and reply-all habits multiply transfer, storage, and reading energy.
  • Avoid large attachments: Use shared links for files that many people need, especially presentations, images, and videos.
  • Compress images and PDFs: Smaller files lower transfer and storage totals.
  • Unsubscribe from unread newsletters: Stopping messages before they are sent is better than deleting them later.
  • Shorten retention for bulky folders: Old attachments are where storage cleanup has the clearest effect.
  • Avoid high-volume email blasts: Mailing list hygiene matters because each recipient copy has a footprint.

Trust and freshness

Last reviewed10 June 2026
Data sourcesCarbon Literacy Project, Mike Berners-Lee estimates, Statista-style email volume reporting, data-centre and network energy modelling defaults.
PrivacyRuns in your browser. Inputs are not uploaded.
Estimate, not an auditResults vary by device, service provider, grid mix, file size, recipient count, and retention policy.

Email Carbon Footprint FAQ

How much CO₂ does one email produce?

Published benchmarks vary widely. The Carbon Literacy Project cites about 0.03 g CO₂e for spam filtered before the inbox, around 0.2 g for a short phone email, around 0.3 g for a short laptop email, around 17 g for a long laptop email, and around 26 g for a high-effort email blast.

Do attachments increase emissions?

Yes. Attachments add data transfer and storage, and every recipient receives a copy. Large photos, PDFs, and presentations are usually the biggest driver in this calculator.

Does deleting emails reduce carbon footprint?

Deleting mail can reduce future storage energy, especially for bulky folders and old attachments. The savings are usually modest per person, but retention rules and cleanup matter more for large inboxes and organizations.

Is email worse than messaging?

Not automatically. The footprint depends on message size, attachments, storage, device use, recipients, and the service behind it. A short text message may be lower than a long email with attachments, while high-volume chat media can also add up.

Does unsubscribing help?

Yes, if it stops unread newsletters and automated mail from being sent, stored, filtered, and occasionally opened. Mailing list hygiene is one of the clearer ways to reduce unnecessary email traffic.

What is CO₂e?

CO₂e means carbon dioxide equivalent. It expresses different greenhouse gases as one comparable climate-impact number.

Why do estimates vary so much?

Estimates vary because devices, data centers, networks, grid carbon intensity, message size, attachment size, retention time, and recipient count all differ. Older benchmark numbers can also be higher than modern energy-intensity estimates.

Do results include device manufacturing?

No. This calculator estimates operational energy from sending, transferring, storing, and reading email. It does not allocate the embodied emissions from making phones, laptops, servers, or network equipment.

Do you store my inputs?

No. Everything runs locally in your browser; nothing is uploaded.

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