Every carbon credit is issued under a standard. The standard decides which projects qualify, how their tonnes are counted and who checks them. Knowing the main standards helps you read a project listing and ask the right questions before you buy.
This page is part of our Learn section. For how a standard’s rules turn into credits, see how carbon credits are created.
What does a carbon standard do?
A standard, also called a carbon-crediting program, does four jobs:
- Sets the rules projects must meet, including how to show the project is additional and how to deal with risks such as reversals.
- Approves methodologies, which set out detailed procedures and peer-reviewed formulas for quantifying a project’s benefitsSource 7.
- Oversees independent audits: validation of the design and verification of results.
- Issues and tracks credits in its registry. See carbon registries.
Under Verra’s VCS, for example, one Verified Carbon Unit represents one tonne of CO₂e, and when a unit is retired it is taken out of circulation so it can be used only onceSource 7.
The main standards compared
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| Standard | Origin | Credit | ICVCM CCP-Eligible |
|---|---|---|---|
 Verra (VCS) | Founded 2007 | VCU | Yes, May 2024 |
 Gold Standard | Founded 2003 by WWF and other NGOs | VER | Yes, April 2024 |
 ACR | Registry since 1996; part of Winrock International | ACR credit | Yes, April 2024 |
 Climate Action Reserve | Began as the California Climate Action Registry, 2001 | CRT | Yes, April 2024 |
 Puro.earth | Removal standard and registry backed by Nasdaq | CORC | Yes, December 2025 |
 Isometric | Founded 2022 | Isometric credit | Yes, December 2024 |
Logos identify the organisations named; no endorsement is implied.As of Oct 2026
Sources: VerraSource 6, Gold StandardSource 8Source 16, ACRSource 11, Climate Action ReserveSource 12Source 17, Puro.earthSource 18Source 14 and IsometricSource 15; ICVCM decisions on ACR, CAR and Gold StandardSource 2, VerraSource 3, IsometricSource 4 and Puro.earthSource 5.
How the standards differ
Verra runs the Verified Carbon Standard, which it calls the world’s leading voluntary carbon markets program. It reports more than 1.3 billion credits issuedSource 6.
Gold Standard was set up to make sure projects under the UN’s Clean Development Mechanism also contributed to sustainable developmentSource 8. It is a not-for-profit headquartered in GenevaSource 9, and it says every project it certifies contributes to at least three UN Sustainable Development GoalsSource 10.
ACR and the Climate Action Reserve both work in voluntary and compliance markets. ACR lists California’s and Washington State’s cap-and-invest programs and ICAO among its marketsSource 11. The Reserve is an approved Offset Project Registry in California and WashingtonSource 12.
Puro.earth and Isometric focus on carbon removal. A Puro CORC confirms one tonne of CO₂ durably removed from the atmosphereSource 14, and the Puro Standard covers removals onlySource 13. The ICVCM describes Isometric as a standard focused on carbon dioxide removalSource 4. Our page on removal vs avoidance credits explains why that difference matters.
What CCP-Eligible means
The ICVCM sets a common quality bar, the ten Core Carbon Principles, covering governance, emissions impact and sustainable developmentSource 1. It assesses programs and credit categories separately.
A CCP-Eligible program meets the criteria for effective governance, transparency, tracking and robust independent validation and verification. It can then use the CCP label on credits issued under methodologies the ICVCM has approvedSource 2.
Program approval is not credit approval
A credit from a CCP-Eligible program does not automatically carry the CCP label. The ICVCM must also approve the methodology category, and its reviews look at categories, not individual projects. Project-level checks still matter.
How to judge a standard when you buy
Step 1: Name the standard
Ask which program issued the credits. If the seller can’t say, stop there.
Step 2: Check its status
Is the program CCP-Eligible, and does the credit category carry the CCP label?
Step 3: Look up the project
Find the project in the standard’s public registry and read its documents and verification reports.
Step 4: Match the type to your goal
Decide whether you want removals, avoided emissions or a mix, and check the standard covers that type.
A good standard is a starting point, not proof that every project under it is sound. Our guide on whether carbon offsets work covers what research has found, and how to verify carbon credits shows how to check a specific purchase. As always, reduce your own emissions first.