22 – Energy Efficiency (Website Carbon Calculator)
The more data a page sends, the more energy is consumed in networks, servers and the visitor's device. The test measures the volume and converts it into carbon dioxide per page view.
What is tested?
- Data transferred during a page visit
- Carbon dioxide per page view, estimated from that volume
- Renewable energy: whether the site's host appears to run on renewable electricity
- Comparison: how the page compares to the other websites tested by Webperf.se
How it's calculated
The model comes from the Website Carbon Calculator and assumes that
- 1.805 kWh is consumed per gigabyte transferred,
- 75 per cent of visitors are returning and already have most of the site cached,
- a returning visitor re-fetches about 2 per cent of the page's data, and
- the electricity grid produces 475 grams of carbon dioxide per kWh.
The comparison figure says what percentage of tested websites the page is greener than. It is refreshed periodically from Webperf's own measurement database. The date it was last updated appears in the review.
How it affects the score
| Score | Meaning |
|---|---|
| 5.0 | The page generates very little carbon dioxide |
| 4.0 | Generates little carbon dioxide |
| 3.0 | About average |
| 2.0 | More carbon dioxide than is preferable |
| 1.0 | A lot of carbon dioxide per page view |
Running the test
python default.py -u https://example.com -t 22 -r
Worth knowing
The test shares a Sitespeed run with the performance test. Run them together and the page is measured once.
Not being able to verify renewable energy isn't the same as the electricity not being renewable. It means the host isn't in the registers consulted.