Guides
Plain-English explanations of the numbers behind every 17x7 calculator — the formulas term by term, worked examples with real figures, and the mistakes that cost people money.
For online sellers
How Etsy Fees Work in 2026
Listing, transaction, processing, Offsite Ads, Share & Save and the fees that only apply outside the US — what each one is charged on, and three orders worked through to the cent.
How to Price Etsy Products for Profit
Start from what an item really costs you, decide what you need to keep, and work back to a list price that survives Etsy's fees — including orders that arrive through Offsite Ads.
Amazon FBA Fees Explained (2026)
Size tier, shipping weight, price band, season and surcharge: the five things that set an FBA fulfillment fee, plus referral and storage fees, worked through on real boxes.
How to Calculate Amazon FBA Profit Margin and ROI
Turn Amazon's fees into the numbers that decide whether a product is worth stocking — profit per unit, margin and return on investment — and see what moves them.
For contractors and DIY builders
How to Calculate Roof Pitch, Rafter Length and Shingles
From a level and a tape measure to a shingle order: how pitch, the pitch multiplier, rafter line length and roofing squares fit together, with three roofs worked through.
How to Estimate Deck Materials
A materials takeoff you can check by hand: rows of decking, cut-aware board counts, joists and hangers, fasteners, and the code span limits that decide joist size.