About PrepperMath

PrepperMath is a free set of calculators and guides for household emergency preparedness. It exists because most prepping advice is either a shopping list or a mood, and neither tells you how much water your household actually needs for fourteen days, or whether the generator you are about to buy will start your well pump. Everything runs in your browser, with no sign-up and nothing to install. The site carries affiliate links; how it is paid for is spelled out below, partner by partner.

Arithmetic, not fear

Preparedness is mostly a storage and consumption problem, and storage and consumption problems are arithmetic. How many gallons, for how many people, for how many days, in what containers, rotated on what schedule, at what cost. Those questions have real answers that depend on your household rather than on a listicle's assumptions. The tools here compute them and show the working, so you can change an assumption you disagree with and see what it does.

Calculators: water storage sizes your supply from household size and target duration; generator sizing works from the actual starting and running watts of what you intend to power, which is where most generator purchases go wrong; and 72-hour kit math turns the standard recommendation into a concrete per-person list.

Guides

Water: purification methods compared and storage containers compared. Food: rotating storage with FIFO, freeze-dried versus canned economics, and blackout food safety, which is the one that matters within hours rather than years. Power: outage planning, generator fuel storage rules and EMP basics. Planning: a family communication plan, evacuate or shelter in place, prepping on a budget, apartment prepping, common mistakes and a seasonal readiness audit.

What this is not

This is not emergency advice and it is not a substitute for official instructions. In an actual emergency, follow your local emergency management authority, and in the United States consult ready.gov and your state or county guidance rather than a calculator. Nothing here is medical, legal, structural or electrical advice: generator installation and fuel storage in particular are governed by local code and by manufacturer instructions, and getting them wrong kills people through carbon monoxide and fire. Where a topic has a real safety floor, we say so on the page rather than leaving it to the reader.

How this site is paid for, specifically

PrepperMath is free. It is supported by display advertising and by affiliate relationships, and we would rather name them than gesture at them. We participate in the My Patriot Supply affiliate programme and link to EMP Shield; if you buy after following one of those links we may earn a commission at no additional cost to you. That is a real financial incentive and you should weigh our recommendations knowing it exists.

What that incentive does not do is change a number. A calculator here computes the same result whether or not you ever click a product link, and we would rather tell you that a cheaper option or no purchase at all is sufficient than manufacture a need. If you ever find a page where the recommendation looks like it was written by the commission rather than the arithmetic, tell us and we will fix it.

Who runs it

PrepperMath is operated by Crossroads Technologies, LLC, a small independent publisher of free web utilities. We are not affiliated with FEMA, the Red Cross, or any government or relief agency, and we do not sell preparedness products ourselves. Corrections and requests are welcome through the contact page.