When choosing how to help others, we often compare trade-offs: Should we support a global health charity or a campaign to ban battery cages for chickens? Most people agree that suffering matters, but how much does animal suffering matter, especially compared to human suffering?

The Moral Weight Project from the non-profit organization Rethink Priorities aims to answer that question. The researchers spent over a year reviewing evidence about how different species experience pleasure and pain, including farmed animals like chickens, pigs, and fishes, as well as humans. Their goal was to estimate the welfare range of each species — that is, how good or bad an individual’s experiences can be.

The project helps advocates assess which strategies and reforms might make the biggest difference for animals. Though the results come with uncertainty, they highlight just how deeply many animals may be capable of feeling — and how urgent it is to improve their lives.

What Is A Welfare Range?

The project is based on a simple ethical idea: If two beings are experiencing the same level of suffering or happiness, then their suffering or happiness should count equally, no matter what species they belong to. What matters morally is the experience itself, not who’s having it.

But, of course, different beings have different mental capacities. Some may be capable of extreme pain or joy, while others may only feel mild discomfort or contentment. A being’s welfare range refers to how wide their possible range of experiences is — from their worst moments to their best. The broader the range, the more a being has at stake, morally speaking. Improving life for a being with a larger welfare range can make a bigger difference because there’s more room for improvement in their experiences.

Estimating Welfare Ranges

To estimate welfare ranges, the team reviewed evidence across 11 farmed animal species, including:

• Pigs and chickens (terrestrial vertebrates)
• Bees, silkworms, and black soldier flies (terrestrial invertebrates)
• Carp and salmon (aquatic vertebrates)
• Octopuses, crabs, crayfishes, and shrimps (aquatic invertebrates)

They examined 90 welfare-relevant traits across categories such as:

• Sensory processing (e.g., ability to detect harmful stimuli)
• Learning and memory
• Emotional responsiveness
• Cognitive abilities
• Social complexity

For each trait, the team looked at existing scientific studies to assess whether the species showed evidence of having that trait. They used cautious scoring — if the evidence was unclear, the trait was either marked “unknown” or excluded.

Once all the chosen species were scored, computer models and simulations were used to estimate their welfare ranges relative to humans. These estimates drew on the trait scoring data and were calculated to reflect uncertainty and data gaps.

What Animals Might Feel

The results were quite surprising. A number of animals came out with much higher welfare ranges than many people might expect.

• Pigs: Around 50% of the human welfare range
• Chickens: Around 30 to 35%
• Octopuses: Around 20 to 25%
• Crayfishes and crabs: Around 5 to 15%
• Carp and salmon: Around 5 to 10%
• Bees, silkworms, and black soldier flies: Less than 10%

In other words, the researchers estimate that a chicken in extreme conditions might experience about one-third the suffering of a human in comparable conditions.

The picture is murkier for insects and other invertebrates partly due to limited research. Still, octopuses scored relatively high given their well-known intelligence. Crustaceans like crayfishes and crabs showed some evidence of pain sensitivity and learning. Even insects like bees showed signs of responsiveness to harmful stimuli.

Challenges And Limitations

While the Moral Weight Project offers a valuable framework for comparing welfare across species, it also comes with important limitations. First, scientific data on many traits are limited or inconsistent, especially for less-studied animals like insects and crustaceans. Some traits were marked “unknown” due to a lack of evidence, making the resulting scores conservative and incomplete, possibly reflecting gaps in research more than real limits in capacity.

Second, the results depend on modelling choices, including how to interpret different traits and how much weight to give different assumptions and theories. The team made these assumptions explicit, and they explored a range of frameworks to account for disagreement and uncertainty. Readers who prefer alternative frameworks may reach different conclusions.

Third, there’s inherent uncertainty in estimating the subjective experiences of non-human animals. We can’t ask a pig or a bee how they feel, so all estimates are indirect. Still, the researchers argue that uncertainty strengthens the case for moral action: if there’s a chance that animals suffer deeply — and we can effectively help them cheaply — then the risk of ignoring them may be greater than the risk of acting.

Overall, the findings should be interpreted as working estimates, not final answers. As more research becomes available, these estimates can be refined. But, for now, they offer a transparent, structured alternative to intuition or bias.

Implications For Animal Advocacy

The Moral Weight Project highlights why animal welfare should be taken seriously as a moral priority grounded in evidence. If many animals are capable of intense suffering or joy, then their well-being deserves greater attention in funding, research, and policy.

The findings also offer a tool for guiding intervention strategies. Welfare range estimates can be incorporated into cost-benefit analyses to help identify where limited resources are likely to do the most good, based on both the number of animals affected and how much those animals may benefit. By estimating how much different animals can feel, this research helps advocates make more informed, strategic decisions about where to focus their efforts.

The Moral Weight Project doesn’t offer the final answer to how much animals matter. But it provides a structured, science-based starting point. By reviewing 90 traits across 11 species, the researchers offer one of the most thorough comparisons of welfare capacity to date, which advocates can use to guide their approach to improving animals’ lives.