Guides & how-tos
Practical answers with the math shown — every guide pairs with a free calculator. Written by Mohamed Zakrya.
Dates & Time
How Time Card Rounding Changes Your Overtime Pay
The same 70 minutes of rounding is worth $25.67 in one week and $38.50 in the next. Nothing changed but the total.
August 15, 2026 · 10 min read
Math
Percentage Difference vs Percentage Change: Which One Do You Want?
40 and 60 are 40% apart, 50% more, and 33.3% less. All three are correct. The denominator is the decision.
August 15, 2026 · 9 min read
Electricity & Energy
What Size Solar System Do I Need to Go Off Grid?
7 panels cover a 10 kWh day with 0.08 kWh to spare. Refilling the battery on that surplus takes 125 days.
August 15, 2026 · 10 min read
Electricity & Energy
How Long Will a Battery Run My House? The Two Tests It Has to Pass
A 100 Ah battery is 1,200 Wh, 600 Wh of it usable — and none of that says whether your fridge will start.
August 14, 2026 · 9 min read
Electricity & Energy
What Is a Demand Charge? Load Factor and Your Real Rate per kWh
Two businesses on one tariff can pay 22.27 cents and 14.57 cents a kilowatt-hour, decided by nothing but how evenly they drew power.
August 14, 2026 · 9 min read
Electricity & Energy
What Is Power Factor? The Current Your Watts Do Not Show
Watts describe the result. Volt-amps describe the burden — and conductor heating follows the square of the difference.
August 14, 2026 · 9 min read
Finance & Math
How Much Should You Tip? Rates by Situation, With the Math
The customary rates by setting, the three-line formula, and the split order that keeps the tip at the rate you chose.
August 14, 2026 · 12 min read
Finance & Math
How to Calculate a Discount: Sale Prices, Stacked Deals, and Tax
The percent-off formula, the sequential math behind stacked deals, and the discount-then-tax order the register actually uses.
August 14, 2026 · 13 min read
Home Improvement
How Much Paint Do I Need? The Complete Room-by-Room Guide
A gallon covers about 350–400 sq ft — but the real number depends on coats, surface, and sheen. Here's how to get it right, with a room-size cheat sheet and the calculator to do the math for you.
August 14, 2026 · 7 min read
Cooking
Laphing 101: Everything You Need to Know About This Tibetan Delicacy
Laphing is Tibet's spicy cold-noodle street food — slippery mung-bean jelly noodles in fiery chili sauce. Learn its origins, how it's made, and how to make it at home.
August 14, 2026 · 17 min read
Home Improvement
How Many Deck Boards Do I Need? Rows, Gaps and the Fencepost
A six-inch board is three different widths, and the gap between boards is part of what they cover.
August 13, 2026 · 9 min read
Home Improvement
How Many Gallons Is My Pool? Average Depth and the Three-Part Floor
The mean of the shallow and deep ends is exact for one shape of floor, and most pools are not that shape.
August 13, 2026 · 9 min read
Home Improvement
How Many Pavers Do I Need? Pavers, Base, Bedding and Joint Sand
Four quantities come out of one measurement, and the paver count is the easy one — the base is where a patio is usually ordered short.
August 13, 2026 · 9 min read
Home Improvement
How Many Stairs Do I Need? Risers, Treads and the Code Edge
You do not choose the riser height. You choose how many, and the height is whatever the division hands back.
August 13, 2026 · 9 min read
Home Improvement
How Much Carpet Do I Need? Runs, Seams and the Roll Width
A 280 sq ft room takes 352.8 sq ft of carpet, and only 14 of those extra feet are the trim allowance.
August 13, 2026 · 9 min read
Home Improvement
How Much Insulation Do I Need? R-Value, Inches and Bags
The target is an R-value, the depth is inches, and the purchase is bags — and bags never come from the inches.
August 13, 2026 · 9 min read
Home Improvement
How Much Roofing Do I Need? Squares, Bundles and the Pitch Multiplier
The one material on a house where the area you measure and the area you buy are different numbers, and the arithmetic that separates them.
August 13, 2026 · 8 min read
Electricity & Energy
What Size Wire Do I Need? Voltage Drop Over a Long Run
The current goes out and comes back, so a 100 ft run is 200 ft of copper — and moving to 240 V helps twice over.
August 13, 2026 · 9 min read
Home Improvement
How Much Flooring Do I Need? Boxes, Waste & Room Math
Floor area is the easy part. Waste tiers, box coverage, and rounding up are where the order goes wrong.
August 13, 2026 · 7 min read
Travel
How to Claim a Trip Back: Mileage or Actual Cost, Per Diem or Receipts
A method-first guide to choosing vehicle, meal, and lodging claims that match the claimant, governing rules, and available evidence.
August 12, 2026 · 11 min read