Free Sustainability Calculators
Run the numbers on your own home with your own utility rates. Everything runs in your browser — no signup, no email, nothing stored. Free to use and free to link to.
Energy
Solar Panel Payback Calculator
Payback period, net cost after incentives, and 25-year return on a home solar system.
Off-Grid Solar Sizing Calculator
How many watts of panel, how much battery, and what size inverter for a van, RV or cabin.
Home Energy Savings Calculator
Annual savings from LED bulbs, a thermostat setback, and cutting standby power.
Heat Pump vs Furnace Calculator
Running cost against gas, propane, oil or electric heat, plus payback on the install premium.
Transport
Home & Garden
Rainwater Harvesting Calculator
Gallons your roof can collect, the tank size you need, and water-bill savings.
Reusable vs Disposable Payback
How fast any reusable swap pays for itself, and the disposables it avoids.
Low-Flow Water Savings Calculator
Gallons and dollars saved from a low-flow showerhead, aerators and an efficient toilet.
Compost Ratio Calculator
Real carbon-to-nitrogen ratio from your actual materials, and how much to add to fix it.
Cloth vs Disposable Diaper Calculator
True cost of cloth versus disposables including washing, and the break-even month.
Using these on your own site
Teachers, extension offices, sustainability programs and community groups are welcome to link to any of these calculators. They are free, contain no paywall or signup, and we keep the underlying assumptions documented on each page so you can check the math.
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