C Level widgets
Add a carbon calculator to your website
Give your readers a way to work out the climate impact of a flight without sending them somewhere else. It is free to embed, it works on a phone, and it runs the same calculation as the C Level flight carbon calculator.
- Licence
- Free, no account
- Install
- One iframe snippet
- Rates
- UK Government 2026
- Branding
- Custom builds available
Build your flight carbon calculator widget
Change the settings, and the preview updates with them. The embed code below updates too, so the code you copy is always the widget you are looking at.
Make it fit your site
The widget carries its own heading, so it makes sense on a page that does not introduce it. Clear both boxes to remove them.
Advanced
The widget sits in a frame of its own, and a frame cannot read the font of the page around it. So there are two honest choices: the reader's own system font, which sits quietly on most sites, or C Level's Epilogue. Need your own face? That is a custom build.
The builder link reopens this page with these settings, so whoever installs the widget does not have to build it again.
Preview
The widget fills the width you give it. On a phone it lays itself out in one column, which is why the snippet's height is the same for all three widths.
Embed your widget
No account, no emailPaste it into any HTML page. When C Level updates the calculator or the government publishes new rates, your embed picks them up. You replace nothing.
About that height, and how to make it follow the widget
The widget fills the width you give it, but a frame cannot work out its own height. The height in the snippet is measured for a widget nobody has used yet, at every width, including on a phone where the widget lays itself out in one column. When a reader gets a result the widget grows past it and scrolls inside the frame.
Add this line once, anywhere on the page, and the frame follows the widget instead — including when a result appears:
That script does one thing: it sets the height of frames that point at this widget. It reads nothing about your page, sends nothing anywhere, and sets no cookie.
Not rendering as you expect? Send us the page and we will look: [email protected].
Choose a starting style
Six presets for six kinds of site. Pick one to see it working, then load it into the builder and adjust.
See the widget in context
The two placements publishers use most: inside the body of an article, and in a sidebar or resource panel.
Climate
What is the carbon footprint of flying from London to New York?
A one-way economy seat between Heathrow and JFK works out at a little under eight hundred kilograms of carbon dioxide equivalent. Fly the same route in business class and the figure is roughly three times higher, because a business seat takes up more of the cabin floor.
The number moves with the route, the cabin and whether you come back. Rather than list every combination, here is the calculator our readers can use directly:
Two things worth knowing about a figure of this kind. It is an estimate made before the flight, from fleet averages, not a measurement of the aircraft you board. And it includes the extra warming caused by emissions released high in the atmosphere, which many airline calculators leave out.
Travel resources
Guidance for staff booking research travel, including the emissions figure needed for annual reporting.
The compact width fits a 340px column with nothing sliding sideways.
Both examples use the same snippet with different settings. Publishers place the widget as content, not as software.
Useful for your readers. Simple for your team.
Free to embed
No licence fee for the standard C Level widget.
A method you can check
Published rates, published sources, and the working shown under every result.
Works on a phone
One column on a narrow screen, two when there is room. No fixed heights.
Kept current by us
When the rates change, your embed changes with them. You replace nothing.
What it costs
The widget you just built is free. It carries a small "Powered by C Level" line in the footer, we host it and keep the rates current, and you carry the credit. That is the whole trade. Three things you can pay for:
Frequently asked questions
How is the figure worked out?
The widget runs the same calculation as the C Level flight carbon calculator. The great-circle distance between the two airports, a rate set by which countries the flight connects, and a weighting for the cabin the passenger sits in.
The rates are the UK Government's 2026 greenhouse gas conversion factors, published on 11 June 2026 by the Department for Energy Security and Net Zero. Each rate is two published figures added together: the flight itself, including the government's allowance for the warming caused by things other than carbon dioxide, plus the figure for producing and delivering the fuel.
So a reader can reproduce the widget's answer from the published workbook. Aircraft type, how full the aeroplane is, and freight in the hold are not modelled, and the widget says so under every result.
It is an estimate made before the flight, not a measurement. The widget never describes a flight as offset, neutral or compensated, and neither should the page it sits on.
Which set of rates produced a result is recorded against it, so an embed made today and a report written next year agree on where the number came from.
The detail is on the flight carbon calculator, and the rates themselves are published by the government. Source (opens in a new tab).
What does the widget do to my page?
No cookies. The widget sets nothing on your domain and nothing on ours.
No reader data by default. The route somebody types goes to our calculator to be worked out, and nowhere else. If a reader chooses to fund the flight, they enter their own details with us, on our side, and you receive none of it.
It loads late. The snippet queues behind your own content.
It links out. The credit and the method open in a new tab, so your reader keeps their place.
Can I change the colours?
Yes. The builder sets the accent colour used by the button, the labels and the result, and offers a light, a dark and a plain style. Under Advanced you can also set the corner radius, the background, whether the button is filled or outlined, and the typeface.
If you need something the controls do not cover — your own face, a different result layout, your own call to action — that is a custom build rather than a setting.
Will it work on WordPress?
Yes, in a Custom HTML block. The same snippet works in Webflow, Squarespace, Wix, Ghost and hand-written HTML. On WordPress you can also paste the widget's own web address on an empty line and it becomes the widget by itself.
Do I need to update it when the rates change?
No. We host the widget, so when the UK Government publishes new conversion factors your embed uses them. You replace nothing.
Can the C Level credit be removed?
Not on the free widget. The credit is what pays for it. A white-label build reduces or removes it and can carry your own branding instead.
Can a reader pay for the flight's impact inside my page?
Not yet. The builder offers a funding option, and today it is a link to C Level's own calculator where a reader can act. Taking a card payment inside your page needs a commercial arrangement with us first. If that is what you want, say so and we will talk about it.