Guides & how-tos
Practical answers with the math shown — every guide pairs with a free calculator. Written by Mohamed Zakrya.
Home Improvement
Sod or Seed: Which One Your Site Will Actually Let You Use
The five site conditions that settle a lawn-establishment method before cost gets a vote, and how to compare the two orders once they do.
August 12, 2026 · 9 min read
Math
How to Find the Volume of Hollow, Partial, and Composite Solids
A decomposition-first guide to pipes, frustums, domes, and partly filled tanks, with formulas and checks for avoiding geometric and unit errors.
August 12, 2026 · 12 min read
Math
How to Compare Two Data Sets: Center, Spread, and Relative Difference
A practical workflow for deciding whether two sets are comparable, describing their typical values and variation, and reporting differences without overstating them.
August 11, 2026 · 10 min read
Utilities
Putting JSON in a URL: Validate, Minify, Percent-Encode, or Base64url?
A decision guide for flattening, encoding, checking, and safely transporting JSON in a query string.
August 11, 2026 · 9 min read
Dates & Time
How to Schedule a Meeting Across Time Zones Without DST or Date-Line Mistakes
A workflow for choosing, validating, and communicating a meeting time when offsets, calendar dates, and daylight-saving transitions can differ.
August 11, 2026 · 10 min read
Cooking
How Many Grams in a Cup? Every Ingredient, One Chart
One formula, fourteen densities. Why flour is 120 g, honey is 340 g, and the ingredient — not the cup — decides the number.
August 10, 2026 · 14 min read
Finance & Math
How Are Loan Payments Calculated? Amortization, Explained
One level payment, front-loaded interest — the formula worked by hand, the two levers you control, and why the smaller payment is often the costlier loan.
July 23, 2026 · 13 min read
Finance & Math
How Does Inflation Work? The Math That Shrinks Money
One growth factor, two answers — what today's money will buy later, and how many future dollars it takes to keep up.
July 23, 2026 · 13 min read
Finance & Math
How Is Sales Tax Calculated? Rates, Rules, and the Reverse Math
The combined-rate reality, the one-multiplication forward formula, and the division that pulls the tax back out of any total.
July 23, 2026 · 13 min read
Electricity & Energy
How Many Solar Panels Do I Need? Sizing From Your Real Usage
Daily usage divided by what one kilowatt makes in a day, why sun hours dominate the count, and the wattage trade that saves a tight roof.
July 23, 2026 · 13 min read
Electricity & Energy
How Much Does Heating Cost? By Fuel, Per Month, With Math
The watts-times-hours formula, the $63 default month, why every 1,500 W heater costs the same to run, and where gas and heat pumps land.
July 23, 2026 · 13 min read
Electricity & Energy
How Much Does It Cost to Charge an EV? Home vs Public, Per Mile
The three-line formula, the losses you pay for but never keep, and why home charging beats public by two to four times.
July 23, 2026 · 13 min read
Health & Fitness
How Much Protein Do I Need a Day? Grams by Goal and Body Weight
Your weight in kilograms times a goal factor. The factor is the whole story — and the range matters more than the number.
July 23, 2026 · 13 min read
Health & Fitness
How Much Water Should You Drink a Day? Real Numbers, Not the 8-Glass Myth
A baseline from your body weight, two flat top-ups for activity and heat — and why the eight-glass rule is one specific person's answer.
July 23, 2026 · 13 min read
Health & Fitness
How to Calculate Body Fat Percentage: Tape-Measure Math That Works
Three tape measurements, one logarithmic formula, a neutral reference band — and why the free method holds up against a lab scan.
July 23, 2026 · 12 min read
Finance & Math
How to Calculate Take-Home Pay: From Gross to What You Keep
One combined deduction rate, your pay schedule, and a two-minute pay stub calibration — gross to net in two lines of math.
July 23, 2026 · 13 min read
Health & Fitness
What Is TDEE? Total Daily Energy Expenditure, With Real Numbers
The resting floor, the activity multiplier that scales it, and how to read the maintenance number that comes out.
July 23, 2026 · 13 min read
Electricity & Energy
What Size Generator Do I Need? Wattage by Scenario
Running watts plus one surge, times 1.2. The honest tally that gets it right, and the mistake that stalls a generator the moment the compressor kicks in.
July 23, 2026 · 13 min read
Finance & Math
How Does Compound Interest Work? The Math That Grows Money
Interest that earns interest — the formula, the frequency gap, and why steady deposits and time do most of the work.
July 20, 2026 · 7 min read
Home Improvement
How Many Rolls of Wallpaper Do I Need? Pattern Repeat Math
The wall-area takeoff, the usable yield of a roll, and why the pattern repeat decides your order.
July 20, 2026 · 6 min read