How-To Guides
How-To Guides
Step-by-step walkthroughs for using EvvyTools calculators and making better decisions.
How-To Guides
How to Sequence Appliance Startups on a Portable Generator During an Outage
Most portable generators die not from total load, but from two surges colliding. Here is how to plan startup order so the breaker holds.
How-To Guides
How to Project Your Net Worth 10 Years Out Without Lying to Yourself About Returns
How to build a 10-year net worth projection that survives contact with reality, instead of one that quietly assumes a perfect decade of stock returns.
How-To Guides
How to Tell if Your Net Worth Is on Track for Your Age
A practical walkthrough for turning your assets and liabilities into a single percentile-ranked snapshot you can act on.
How-To Guides
How to Tell If a Number Is Prime Quickly by Hand (and When to Stop Guessing)
Divisibility rules, a square-root ceiling, and a short list of small primes is almost always enough to tell whether a number is prime by hand.
How-To Guides
How to Identify an Unknown Material by Measuring Its Density
A practical guide to identifying a mystery material using only a scale, some water, and the density values you can look up in any reference table.
How-To Guides
How Much Electricity Each Appliance Actually Uses at Home
Your electric bill rarely matches your intuition about which devices use the most power. This guide explains how to find the real energy hogs at home and what to do about them.
How-To Guides
Tree Age Estimation: How Trunk Diameter Reveals a Tree's History
Most trees don't come with birth certificates. Here's how to estimate age from trunk size using the same method professional arborists use.
How-To Guides
How to Convert Units of Measurement Without Getting Lost
Understand unit conversion with practical formulas. Covers length, weight, temperature, volume, digital storage, and the key squared-units mistake.
How-To Guides
How to Know If You Are on Track to Retire Comfortably
Are you on track to retire? The answer requires more than checking your 401k balance. Here is how to run the actual calculation correctly.
How-To Guides
Projectile Motion: How to Calculate Any Trajectory
Projectile motion calculations come up in physics class, sports science, and engineering. Here is how to calculate range, height, and flight time accurately.
How-To Guides
How to Calculate Exact Age and Date Differences
Calculating exact age sounds simple until you hit leap years and month boundaries. Here is how date math actually works and where the edge cases hide.
How-To Guides
How to Scale a Recipe Up or Down the Right Way
A practical guide to scaling recipes up or down, including the ingredients that never scale linearly and how to adjust pan size.