Why it matters
Understand
the numbers.
Every figure above has a reason behind it. This is what each one protects against.
One gallon is survival, not living
Federal guidance sets one gallon per person per day as the minimum for drinking and basic sanitation. A household that has to live, cook and wash for months needs more, and hot climates can double drinking needs.
Winter sets the size of the system
Solar arrays and battery banks are sized for the shortest, cloudiest days, not for July. That is why cold-climate estates carry more storage and more backup fuel.
Heat is the winter lifeline
In a cold-climate estate, heating fuel is often the largest single stored resource. Running short in February is not an inconvenience; it is the emergency.
Calories, then variety
Calories keep a household working. Stored food should still be varied: grains, legumes, oils, dried dairy, fruit and the fresh greens a greenhouse provides.
Storage is a building problem
Six months of supplies for a family is measured in thousands of gallons and thousands of pounds. It needs engineered space that stays cool, dry and dark.
Redundancy beats size
Two water sources, two ways to make power and two ways to heat matter more than one oversized system. Our designs layer them.
Method
How we
calculate.
Planning figures, not guarantees. Final systems are engineered for the site, the climate and the household.
Water. Survival minimum is one gallon per person per day (Ready.gov). Our planning rate for long-duration living is three gallons per person per day for drinking, cooking and hygiene, and four in hot climates. A producing well changes how much is stored, but we still keep at least 30 days in reserve for pump or power failure.
Food. Calories per day: adults 2,400, adults over 60 2,000, teens 2,400, children 1,500, close to federal estimates for moderately active people. Pounds assume dry staples at about 1,600 calories per pound. For a person-by-person plan, use the Medicine and Nutrition Planner.
Solar. Daily demand divided by peak sun hours (4 in cold climates, 5 temperate, 6 desert) with a 20 percent allowance for losses. Batteries cover 3 to 5 sunless days at 90 percent usable capacity.
Backup generation covers 6 to 30 percent of the period's energy depending on climate, at about 4 kWh per gallon of propane. Heat is heated square feet times heating degree days times 5 BTU for a high-performance envelope, with the share of the winter the period covers. Propane at about 87,000 usable BTU per gallon; seasoned hardwood at about 14 million usable BTU per cord.
Questions
Common
questions.
How much water should a family store?
The federal minimum is one gallon per person per day. For a family of four over 180 days that is 720 gallons. For daily life including cooking and washing, we plan three gallons per person per day, or 2,160 gallons for the same family.
How big a solar system does an off-grid estate need?
It depends on demand and climate. A typical estate using about 45 kWh a day in a cold-winter region needs roughly a 14 kW array and around 250 kWh of batteries to ride through five sunless days, plus backup generation.
Why does the calculator include propane even with solar?
Because winter. Short days and snow-covered panels mean a cold-climate estate needs backup generation, and propane stores for years without degrading.
Can I rely on a well instead of stored water?
A good well is the best long-term water source, but pumps and power fail. We always pair a well with stored reserves and a non-electric way to draw water.
Private Consultation
Bring us
your numbers.
Send your results with a consultation request and we will walk through them with you, privately and without obligation.
More planning tools
Days of Independence
Enter what your property holds today and see how many days your family could stand on its own, resource by resource.
Open HealthMedicine and Nutrition Planner
Build your household person by person: calories, medical conditions, cold storage, medical power and potassium iodide doses.
Open Below gradeShelter Configurator
Size below-grade quarters for your household: square footage by room, filtered air, earth cover and protection factor.
Open