Guides
One question per guide, answered with real numbers and a link to the tool that does the job. No signup, and the tools run in your browser.
Images
3 guides- JPG vs PNG vs WebP vs AVIF: Which Format to Use Which image format for photos, logos, transparency and animation. Browser support, typical file sizes with sources, and when to convert. Read the guide
- How to Compress a Photo Under 100 KB Get a photo under 100 KB in three steps: resize, then lower the quality, then pick the format. Which pixel sizes fit, and how upload forms check the size. Read the guide
- HEIC Photos Explained: Open, Convert, Avoid What a HEIC file is, why Windows and upload forms reject it, how to convert it to JPG or PNG in your browser, and how to make an iPhone shoot JPG. Read the guide
Money
2 guides- Margin vs Markup: Formulas, Table and Examples Margin divides profit by price, markup divides it by cost. The formulas, a markup-to-margin table from 10% to 300%, worked examples and common mistakes. Read the guide
- How to Calculate Sales Tax The sales tax formula with real 2026 state rates: add tax to a price, back it out of a receipt total, round to the cent, and how it differs from VAT. Read the guide