Off-Grid & Rural Calculators
Ten free calculators for the infrastructure side of rural life: water, power, heat, waste and equipment. Many of these decisions are expensive to get wrong, so each calculator shows its assumptions and the source behind its numbers.
Firewood Cord & BTU Comparator
Compare heat value and real delivered cost per million BTU across wood species — and against propane, heating oil, electric, and natural gas.
Fur/Pelt Trapping Value Calculator
Estimate what your pelts might bring across 21 commercially harvested North American fur species, using 2025–26 season average auction prices.
Generator Size Calculator
Size a backup generator based on the appliances and circuits you actually want to keep running.
Rain Barrel / Cistern Sizing Calculator
Estimate how many gallons you can harvest from your roof, and what size storage you'd need to capture it.
Sawmill Log-to-Board-Feet Calculator
Estimate lumber yield from a log's small-end diameter and length, using the three standard forestry log rules.
Septic Tank / Leach Field Sizing Calculator
Estimate septic tank capacity and leach field area from bedroom count and soil percolation rate — the same approach county health departments use for...
Solar & Battery Bank Calculator
Size an off-grid solar array and battery bank based on your daily energy use and days of autonomy.
Tractor PTO Horsepower & Implement Sizing Calculator
Match a rotary cutter's width to your tractor's PTO horsepower — and find out roughly what your engine's rated HP actually delivers at the PTO.
Water Trough De-Icer Sizing Calculator
Match de-icer wattage to your stock tank size, so livestock water stays open all winter without overspending on electricity.
Well Pump Sizing Calculator
Match pump horsepower to your well depth, household demand, and desired water pressure — using the real hydraulic engineering formula, not a rule of...
Water
Water systems are planned from demand backward. The well pump sizing calculator turns household and livestock demand, well depth and pressure needs into a pump size, and warns about the common mistake of oversizing, which short-cycles the pump and shortens its life. The rain barrel and cistern calculator estimates how much a roof can collect from local rainfall. Livestock owners in cold climates can use the water trough de-icer calculator to size a heater to the trough and the lowest temperature.
Power
Off-grid power starts with the load. The generator size calculator adds running and starting watts for the equipment you want to power, since motors draw several times their running load for a moment at startup. The solar and battery bank calculator then sizes panels and storage to your daily energy use. The two tools together tell you whether a generator is a backup or the main source.
Heat and wood
The firewood cord and BTU comparator compares species and cord sizes by heat delivered, which matters because a full cord of hardwood can deliver far more heat than a full cord of softwood. The Firewood Species Finder helps you pick a species to cut or buy. If you mill your own lumber, the sawmill log-to-board-feet calculator estimates yield from a log.
Waste, equipment and income
The septic tank and leach field calculator gives a planning estimate of tank size and field area. It is not a design, and a local health department or licensed installer must approve any system. The tractor PTO calculator checks whether a tractor's power can run an implement, and the fur and pelt trapping value calculator estimates returns for those who trap lawfully.
Fencing
For fence planning, see the fence post calculator on LumberCalcs, which covers post counts and spacing in detail.
Codes, permits and professionals
Wells, septic systems, electrical work and wood stove installations are regulated almost everywhere. County health departments, building departments and insurers set their own requirements, and they differ by location. Use these calculators to understand the scale of what you need and to ask better questions, then confirm sizing and permits with the people who inspect and insure the work. See our disclaimer for the full wording. For a plain-language walkthrough, read the off-grid water and power guide and the guide to heating with wood.
Common questions
Do I still need a professional if the calculator gives me a number?
For wells, septic and electrical work, yes. The numbers help you plan, budget and ask good questions. A licensed installer or inspector still has to size, install and approve the system under your local code.
Which tool should I run first?
Start with demand: how much water, power or heat you actually need. Every other tool in this section follows from that. For example, the generator size calculator tells you which loads to count before you size a battery bank.