The CO2 Math of Switching a Commute to an E-Bike or E-Scooter

“Riding instead of driving cuts your carbon footprint” is true directionally, but the honest question is by how much, and that depends entirely on the assumptions behind the arithmetic. Rather than quoting a figure from an unnamed source, this article works from the same assumptions our own CO2 savings calculator uses, stated plainly, so you can see exactly what is being estimated and adjust it if your own numbers differ.

Why "how much CO2 do I save" needs a specific answer, not a slogan

Generic claims that riding "is better for the environment" are true but unhelpfully vague — they give no sense of scale, and vague claims are exactly where people either overestimate or dismiss the impact of a single behaviour change. A specific, worked figure lets you judge for yourself whether the saving from your own commute is meaningful relative to your other choices, rather than relying on a feeling one way or the other.

The assumptions behind the number, stated plainly

The calculator’s default assumption is that a typical petrol car emits about 170 grams of CO2-equivalent per kilometre on a well-to-wheel basis (accounting for the fuel burned to move the car), and that a micro-mobility vehicle’s share of the emissions from generating the electricity it charges on works out to roughly 8 grams of CO2-equivalent per kilometre on an average grid. These are the calculator’s own stated assumptions, not figures attributed to a specific study, and they will not match your own car or your own electricity grid exactly — a more efficient or less efficient car, and a cleaner or dirtier local grid, both shift the real number. Treat them as reasonable, adjustable starting points rather than precise measurements of your specific situation.

Worked example: an 8 km commute

Run an 8 km one-way commute, ridden 10 one-way legs a week for 50 weeks a year, through the CO2 savings calculator at its default assumptions, and it returns an annual distance of 4,000 km, car emissions of 680 kg CO2 for the year, micro-mobility emissions of 32 kg, and a saving of 648 kg of CO2 a year — equivalent, using the calculator’s tree-absorption estimate, to roughly 31 mature trees’ worth of annual CO2 uptake.

Worked example: a 15 km commute

Stretch the same weekly pattern to a 15 km one-way commute and the annual distance rises to 7,500 km. The car’s annual emissions rise to 1,275 kg, micro-mobility’s to 60 kg, and the saving to 1,215 kg of CO2 a year — about 58 trees’ worth. The saving scales almost exactly with distance, which makes sense: both emissions figures in the calculator are per-kilometre, so doubling the distance very nearly doubles the saving.

Worked example: a short 3 km commute

At the other end, a 3 km one-way commute on the same weekly pattern comes back with an annual distance of 1,500 km, car emissions of 255 kg, micro-mobility emissions of 12 kg, and a saving of 243 kg — about 12 trees’ worth. Even a short commute adds up meaningfully over a full year of repetition, which is really the whole point of measuring this annually rather than per trip: 243 kg sounds modest for one year, but it compounds over every year you keep riding.

A quick way to read the calculator's output

The calculator returns five figures, and it helps to know what each answers. Annual distance is simply how far you cover in a year at your stated trip pattern — the common baseline the rest of the figures are built on. Car and micro-mobility annual kilograms are what each mode would emit covering that same distance, so you can see both sides rather than just the difference. Saved kilograms is the headline number, the gap between those two. Trees-equivalent is purely a way to make that gap intuitive, not a literal count of trees you should plant. Reading all five together, rather than jumping straight to the saved-kilograms figure, makes it clear the saving comes from replacing a genuinely large car footprint with a genuinely small micro-mobility one, not from some other adjustment.

Why the gap between car and micro-mobility is so large

The size of the gap comes down to two different ways of moving a person. A car burns fuel directly, in an engine that is inherently inefficient at turning chemical energy into motion, to move a vehicle that typically weighs well over a tonne. A micro-mobility vehicle draws a comparatively tiny amount of electricity to move a machine that, rider included, weighs a small fraction of that — and electric motors convert stored energy into motion far more efficiently than an internal combustion engine does. Both factors point the same direction, which is why the per-kilometre gap is large rather than marginal.

What this estimate leaves out

In the interest of being straightforward about the limits of this arithmetic: the calculator’s emissions figures cover the energy used to move the vehicle, not the emissions embodied in manufacturing it in the first place. Building any vehicle — a car, an e-bike, or an e-scooter — has its own carbon cost, and that is not part of this per-kilometre estimate. The 8 g/km micro-mobility figure is also an average-grid assumption; if your local electricity generation is unusually clean or unusually carbon-intensive, your real figure will differ from the calculator’s default in either direction. None of this changes the direction of the result — riding instead of driving a given distance reduces the emissions from that distance — but it is worth being precise about what is and is not being measured.

The tree figure is a communication tool, not a literal equivalence

The “equivalent to N trees” figure uses the calculator’s own stated estimate that a mature tree absorbs roughly 21 kg of CO2 a year, purely to translate a kilogram figure into something more intuitive. It is not a claim that planting a specific number of trees offsets your commute, nor a substitute for a rigorous carbon-offset calculation — tree absorption rates vary hugely by species, age, and climate, and a newly planted sapling absorbs far less than a mature tree for years. Treat it as a way to get a feel for the scale of the saving, not as an input to any formal offsetting claim.

What actually moves your own number

Three inputs drive the whole calculation: your one-way distance, how many one-way trips you make a week, and how many weeks a year you keep it up. Doubling any one of them roughly doubles the annual saving, since the underlying formula is a straightforward multiplication. If you only ride two or three days a week rather than a full five-day pattern, or you take weeks off in winter, plug your real trip count into the CO2 savings calculator rather than assuming the full-time figures above apply to your actual routine — a partial switch still saves real CO2, just proportionally less than switching every trip.

What a partial switch actually looks like

Few people go from driving every day to riding every day overnight, and the calculator handles that gracefully — the trips-per-week input is exactly for this. Take the 8 km commute from the first worked example, but instead of 10 one-way trips a week, model riding just 3 days a week (6 one-way trips): the annual distance drops to 2,400 km, and the saving scales down proportionally to about 389 kg of CO2 a year, still a meaningful figure for a partial commitment. The broader point is that the CO2 saving from riding is not an all-or-nothing outcome — every trip you ride instead of drive contributes its share, so a partial switch is worth doing even if a full one isn’t realistic for your circumstances right now.

Transit's own emissions are outside this calculator's scope

This calculator specifically compares a car against micro-mobility; it does not model a transit trip's emissions, because those depend heavily on the specific vehicle, its occupancy, and the local grid or fuel mix powering it — a nearly-empty bus and a nearly-full train have very different per-passenger footprints even covering the identical route. If your real alternative to driving is transit rather than an e-bike or e-scooter, this specific tool is not the right one to quantify that comparison, and you should be wary of any figure — ours or anyone else’s — that states a single universal number for transit emissions without naming the vehicle type and occupancy assumption behind it.

Multiple commuters, multiplied savings

Everything above is calculated per person, per commute. In a household with more than one person driving to work, school run, or any other regular trip, the same arithmetic applies to each commuter separately, and the household total is simply the sum. A two-commuter household each riding an 8 km one-way trip on the pattern above would be looking at roughly 1,296 kg of CO2 saved a year between them — twice the single-commuter figure, for the same reason that a second car produces roughly a second car’s worth of emissions. If you are estimating a household or workplace-wide figure, run the calculator once per commuter and add the results, rather than trying to average distances that vary between people.

Putting it alongside the money

CO2 savings and cost savings move together for the same underlying reason: both are driven by how much you ride instead of drive. If you are also curious what the same commute saves in money rather than carbon, our guide to the true cost of an e-bike versus a car or transit pass runs the equivalent numbers through the cost calculators, and the commute distance reference lays out time, cost, and CO2 side by side across a whole range of distances at once.