About the Carbon Offset Calculator
This carbon offset calculator converts an amount of carbon dioxide into the things people use to balance it: the number of trees that would absorb it, the area of forest that sequesters it in a year, and the number and cost of carbon credits (one credit usually represents one metric tonne of CO₂e). Enter the emissions in tonnes, kilograms, pounds or US short tons, choose how many years the trees have to do the job, and set the price per credit you have been quoted.
Use it after working out your footprint with the carbon footprint or flight carbon calculators, to budget for offsetting a trip or an event, or simply to understand the scale of a number like “16 tonnes a year”. The chart shows how the number of trees needed falls as you give them more years to absorb the carbon.
Tree absorption varies enormously with species, age, climate and growing conditions. The default of 22 kg of CO₂ per tree per year is a commonly used figure for a mature, healthy tree; young trees absorb far less, which is why the EPA’s equivalency for a seedling grown for ten years (0.060 t in total) is also shown. Offset prices range from a few dollars to over $100 per tonne depending on project type and verification standard, so treat the cost as an estimate.
With the default inputs, the mature trees needed is 728. Change any value above to recalculate instantly.
How to use the carbon offset calculator
- 1Enter the amount of CO₂ you want to offset and choose its unit.
- 2Adjust how much CO₂ one tree absorbs per year if you have a better figure.
- 3Choose how many years the trees have to absorb it.
- 4Enter the price per tonne for the carbon credits you are considering.
- 5Compare the trees, forest area and credit cost.
Formula and method
The amount is first converted to kilograms and metric tonnes (1 t = 1,000 kg, 1 lb = 0.4536 kg, 1 US short ton = 907.18 kg). The number of trees is the CO₂ divided by what one tree absorbs per year times the number of years allowed, rounded up to a whole tree. Credits are one per metric tonne, so the cost is tonnes × price.
Two EPA equivalencies give extra context: an urban tree seedling grown for 10 years sequesters about 0.060 t of CO₂ in total, and an acre of average US forest sequesters about 0.84 t per year. These are averages; actual sequestration depends on species, climate, soil and whether the trees survive long-term.
- kg per tree per year
- Average CO₂ one tree absorbs annually
- years
- Time allowed for the trees to absorb the CO₂
- price per credit
- Cost of a carbon credit representing 1 t CO₂e
Worked examples
Offset 16 tonnes of CO₂ within one year
Sixteen tonnes is 16,000 kg; at 22 kg per tree per year that is 727.3, so 728 mature trees for one year. Sixteen credits at $15 cost $240. It equals about 267 seedlings grown for ten years or 19 acres of forest for a year.
A 2,000 lb flight footprint over 10 years
Two thousand pounds is about 907 kg (0.907 t). Giving trees ten years, 907 ÷ (22 × 10) = 4.1, so 5 trees. At $25 per tonne, credits cost about $22.68.
Company event emitting 120 t, offset over 20 years
Spreading 120,000 kg over 20 years at 25 kg per tree needs 240 trees. Buying 120 credits at $40 would cost $4,800, and about 7.1 acres of forest would absorb it over the same 20 years.
Frequently asked questions
How many trees does it take to offset one tonne of CO₂?+
At about 22 kg of CO₂ per mature tree per year, one tonne takes roughly 46 trees for one year, or about 5 trees over ten years. Young trees absorb much less, so plantings take decades to deliver their full offset.
How much does it cost to offset carbon?+
Voluntary carbon credits commonly sell for about $5–$50 per tonne, while high-quality removal credits such as direct air capture can cost several hundred dollars. Offsetting a 16-tonne yearly footprint therefore ranges from under $100 to thousands.
What is one carbon credit?+
A carbon credit usually represents one metric tonne of CO₂ or CO₂-equivalent that has been avoided or removed from the atmosphere by a verified project. Look for standards such as Verra (VCS) or Gold Standard and check that credits are retired in your name.
Is planting trees a good way to offset emissions?+
Trees help, but the carbon is only stored while they live and they absorb slowly while young. Offsets work best alongside reducing emissions, and tree projects should guarantee long-term protection against logging, fire and disease.
How much CO₂ does an acre of forest absorb?+
The US EPA uses about 0.84 metric tonnes of CO₂ per acre per year for an average US forest. Fast-growing tropical or young managed forests can absorb more, while old or dry forests often absorb less.