About the Online Shopping Footprint
This calculator weighs the carbon cost of a solo car trip to a physical store against a shared home delivery, on a per-item basis. It is built for shoppers who order online out of convenience but wonder whether a quick drive to a nearby store would actually be the lower-carbon way to pick up just one or two things.
How It Works
You enter the round-trip mileage to the store you would normally drive to, roughly how many items you tend to buy per trip, and your car's fuel economy. The tool converts the gas burned on that drive into kilograms of CO2, then divides it across the number of items purchased so a single item's share of the trip's emissions can be compared directly to a fixed per-package estimate for a shared delivery van.
Formula & Methodology
The 8.887 figure is the standard kilograms of CO2 released per gallon of gasoline combusted. Dividing round-trip miles by mpg gives gallons burned for the whole trip, and multiplying that by 8.887 converts it to a total trip footprint in kilograms. Because that emissions total belongs to the entire trip rather than any single item, the calculator spreads it evenly across however many items you typically buy per outing - a trip for one item carries the full weight of the drive, while a trip for a dozen items spreads that same footprint twelve times thinner. The delivery side of the comparison is deliberately simpler: rather than modeling a specific van route, it applies one flat per-package figure meant to represent a van already loaded with many other stops on its route.
Examples
A short, well-loaded trip
With the defaults - a 6-mile round trip at 28 mpg for 5 items - the drive works out to about 1.90 kg of CO2 total, or roughly 0.38 kg per item, undercutting the 0.50 kg delivery estimate.
A longer drive for a small haul
A 10-mile round trip at 20 mpg for just 3 items produces about 4.44 kg of CO2 total, or roughly 1.48 kg per item, nearly three times higher than the 0.50 kg delivery figure.
Advantages
- Turns an abstract delivery-vs-driving debate into a concrete per-item number using your own car and driving distance.
- Highlights how much cart size matters - the same drive looks very different environmentally depending on whether you buy 2 items or 12.
- Uses a single transparent input set (distance, items, mpg) so the comparison is easy to recompute for different stores or vehicles.
Common Mistakes
- Entering one-way distance instead of round-trip distance, which understates the true driving footprint by half.
- Assuming online orders are always lower-carbon without adjusting for cart size - a single-item order can outweigh a nearby car trip loaded with purchases.
- Ignoring that combining multiple planned errands into one drive changes the effective items-per-trip figure and can shift the result significantly.
Edge Cases to Watch For
- If items per trip is left at zero, the calculator floors it at one so the division does not break, which can understate how efficient a genuinely large shopping trip is.
- Fuel economy is floored at 1 mpg if entered as zero, which produces an extreme driving footprint rather than a calculation error.
- The fixed 0.5 kg delivery estimate assumes ground shipping on an already-efficient route; it does not account for air freight, rural last-mile delivery, or a van running under capacity, all of which raise the real per-package figure.
- Combining several errands into one car trip is not modeled as a separate input - you would need to raise items per trip to reflect the extra stops covered.
Common Use Cases
- Shoppers deciding between a quick errand and ordering a single item online.
- Households trying to understand how batching purchases into fewer, larger online orders (or fewer, larger car trips) affects their footprint.
- Anyone curious how their specific car's fuel economy changes the driving side of the delivery-versus-driving tradeoff.