Guides & how-tos
Practical, number-heavy guides that teach the math behind the calculators — so you can estimate with confidence even when the internet is not around.
October 22, 2026 · 7 min read
How to Estimate Concrete: Yardage, Bags, and Ordering Without the Guesswork
Concrete is ordered by the cubic yard and paid for by the truckload. Here is the exact math for slabs, footings, and bag counts — plus the waste factor pros actually use.
Read guideOctober 22, 2026 · 6 min read
Roof Pitch Explained: What 6/12 Really Means and Why It Changes Everything
Roof pitch controls your roof's true area, your shingle count, and your material cost. Learn to measure it, convert it, and use it to estimate a roof like a pro.
Read guideOctober 22, 2026 · 6 min read
Tile Estimation Guide: From Room Measurements to the Exact Box Count
Tile math goes wrong in predictable ways: forgotten waste, pattern repeats, and box sizes that don't divide evenly. Here's the step-by-step method that gets the order right.
Read guideOctober 22, 2026 · 7 min read
Etsy Fees in 2026: The Complete Breakdown With Real Examples
Etsy stacks five separate fees on every sale, and the total is higher than most sellers guess. Here is the full 2026 fee stack with worked examples at three price points — and how to price so you actually keep your margin.
Read guideOctober 22, 2026 · 6 min read
How to Calculate GPA: A Step-by-Step Guide for Students
GPA is a credit-weighted average, not a simple average of grades. Here is the 4.0 scale, a full worked example with five courses, and the difference between weighted, unweighted, semester, and cumulative GPA.
Read guideOctober 22, 2026 · 6 min read
How Much Paint Do I Need? The Exact Formula
Paint math is wall area minus openings, divided by coverage per gallon, times coats. Here is the step-by-step method with a worked 12×14 room example — plus ceiling, trim, and primer rules.
Read guideOctober 22, 2026 · 7 min read
What Is a Good ROAS? 2026 Benchmarks
ROAS is revenue divided by ad spend — but a 'good' ROAS depends entirely on your margin. Learn the break-even formula, realistic benchmarks by business type, and how to actually improve it.
Read guideOctober 22, 2026 · 7 min read
Final Exam Calculator: What Score Do You Need to Pass?
Stop guessing what your final needs to be. Here is the exact weighted-grade formula, a worked example at 82% with a 30% final, and what to do when the math says you need 112%.
Read guideOctober 22, 2026 · 8 min read
Amazon FBA Fees in 2026: The Complete Seller's Guide
FBA typically costs 30–35% of the sale price once every fee stacks — not the 15% most sellers budget. Here is the full 2026 fee schedule, a worked example on a $25 product, and FBA vs. FBM.
Read guideOctober 22, 2026 · 7 min read
SAT Score Chart Explained: Raw Score to Scaled Score
Your SAT score is not a simple percentage — it is your raw correct-answer count run through a per-test conversion table. Here is how 200–800 section scores work, why the same raw score converts differently on different test dates, and a worked practice-test example.
Read guideOctober 22, 2026 · 7 min read
eBay Fees in 2026: What Sellers Actually Pay
eBay's headline fee is 13.6%, but the real cost of a sale includes a per-order fee, international surcharges, optional ad rates, and category exceptions. Here is the full 2026 fee stack with a worked $50 example.
Read guideOctober 22, 2026 · 7 min read
How to Calculate Board Feet of Lumber (With Examples)
Lumber is priced by the board foot, not the board. Learn the one formula, see worked examples for common sizes, and avoid the nominal-vs-actual trap that trips up beginners.
Read guideOctober 22, 2026 · 7 min read
Profit Margin vs Markup: The Difference That Saves Businesses
A $20 cost sold for $30 is a 50% markup but only a 33.3% margin. Mixing the two up is one of the most expensive mistakes in pricing — here is how to keep them straight.
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