Sustainable software engineering can benefit the environment and operations when it delivers the same useful work with less electricity or fewer hardware resources. That is a practical possibility, not a guaranteed cost saving: teams need to measure both environmental impact and cost for the workload they are changing.
What is sustainable software engineering?
Software runs on physical hardware, so its environmental footprint is not limited to the code itself. Running applications consumes electricity, and the emissions associated with that use depend on where and when the electricity is generated. The hardware needed to run software also has embodied emissions from its manufacture.
The Green Software Foundation identifies the Software Carbon Intensity (SCI) specification as ISO/IEC 21031:2024. SCI expresses emissions in relation to a meaningful unit of useful work:
SCI = (E × I + M) per R
- E is the energy consumed.
- I is the carbon intensity of the electricity used.
- M is the embodied emissions of the hardware required.
- R is a functional unit, such as a transaction, user, or API call.
This framing helps teams ask not only how much energy a system uses, but how much impact is associated with a defined amount of useful work. Read the Green Software Foundation’s SCI overview.
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How can software use less energy and hardware?
The SCI specification groups sustainability work into three engineering levers. They can interact, and their effects should be assessed across the system boundary that matters—not just in the code or component where a change is made.
Energy efficiency
Energy efficiency means using less electricity to perform the same function. For example, a change that reduces computation for each transaction may improve energy use per transaction, provided the workload and useful result remain comparable.
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Hardware efficiency
Hardware efficiency means using fewer physical resources to perform the same function. Better utilization or reduced resource requirements can affect the hardware needed to serve a workload, and therefore may affect both operating needs and embodied emissions.
Carbon awareness
Carbon awareness means adjusting when or where computation runs in response to electricity carbon intensity. It is most applicable when a workload can be shifted or placed flexibly without compromising its purpose or requirements.
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These are not isolated slogans. A local optimization can have a different effect when storage, networking, infrastructure, or user devices are included. The specification puts it plainly: “The SCI takes a systems-impact view.” See the Software Carbon Intensity Specification, version 1.1.0.
How do you measure whether a change helps?
Start with a baseline and compare the proposed change using the same system boundary, functional unit, measurements, assumptions, and models. The SCI specification calls for an identical methodology for the baseline and proposal except for the action being evaluated. SCI is a rate, and lower scores are better; scores built with different boundaries or functional units are not reliable like-for-like comparisons. Consult the SCI specification’s comparison guidance.
- Define the useful work. Choose a functional unit that fits the system, such as one transaction or API call, and use it consistently.
- Fix the measurement boundary. Decide which infrastructure and downstream effects are relevant. Keep that boundary unchanged between baseline and proposal.
- Measure the baseline. Record energy per functional unit, the electricity carbon intensity by location and time, and the hardware required, including its embodied emissions where relevant.
- Make one proposed change. Keep the workload and useful function comparable so the change is the meaningful difference between the two cases.
- Compare SCI and cost. Use the same assumptions and models for both cases. Consider whether any improvement in the rate is accompanied by an operational cost change.
A lower SCI rate indicates lower emissions per chosen unit under the measurement method; it does not, by itself, tell you the total emissions of a growing workload. Keep the functional unit and total workload in view when interpreting results.
Can greener software reduce operating costs?
It can, but the result depends on the workload and the intervention. Using less electricity or requiring fewer hardware resources for the same useful work may reduce operating requirements. Carbon-aware scheduling may use cleaner electricity when a workload can be moved to a different time or place.
Those mechanisms make environmental and operational gains plausible, but they do not establish a universal return on investment. An intervention may have costs or trade-offs, and a carbon improvement does not automatically mean a lower bill. Measure cost and SCI together for the specific workload rather than assuming every sustainability change pays for itself.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What does the broader definition of green software include?
In a 2026 working definition, the Green Software Foundation describes green software as minimizing carbon emissions, energy consumption, water use, and waste across the technology stack, from silicon through user-facing software. These impacts are related, but they are not interchangeable: a carbon-only SCI score does not account for every water or waste impact. Read the Foundation’s discussion of green software’s scope.
What is the status of SCI for Web?
SCI for Web is a domain-specific methodology that the Green Software Foundation described as under development. In an article dated February 3, 2026, the Foundation reported that fourteen member organisations took part in a ten-week design assembly in autumn 2025. That documents active methodology work; it does not establish that a final SCI for Web standard has been published. Read the Foundation’s February 3, 2026 update.
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