17 × 7 = 119 # Calculators that show their work. Free, fast calculators for people who sell and build — Etsy and Amazon fees, roof pitch, deck materials. Every answer comes with the arithmetic behind it, so you can check it, trust it and explain it. - No sign-up - Runs in your browser - Fee schedules dated & sourced - Free to embed ## For online sellers Marketplace fees, margins and the price you need to charge. - [Etsy Fee Calculator](https://17x7.com/tools/etsy-fee-calculator/): Every Etsy fee on one order — listing, transaction, processing, Offsite Ads — and what you actually keep. (`6.5% + 3% + $0.25 + $0.20`) - [Amazon FBA Calculator](https://17x7.com/tools/amazon-fba-calculator/): Size tier, fulfillment fee, referral fee and storage for one unit, with margin and ROI. (`tier(L×W×H, lb) → fee`) ## For contractors and DIY builders Slopes, spans and material takeoffs, with the code limits that apply. - [Roof Pitch Calculator](https://17x7.com/tools/roof-pitch-calculator/): Pitch from rise and run (or angle) plus degrees, slope, rafter length, squares and shingle bundles. (`atan(6 ÷ 12) = 26.57°`) - [Deck Material Calculator](https://17x7.com/tools/deck-material-calculator/): Boards, joists, hangers and screws for a rectangular deck — cut-aware, with the least-waste board length. (`⌈144″ ÷ 5.6875″⌉ = 26 rows`) ## For developers and AI agents The time zone and cron tools also answer over the JSON API and MCP; the JSON Schema, YAML and robots.txt tools run only in your browser. - [Time Zone Converter](https://17x7.com/tools/time-zone-converter/): Convert one moment into up to 20 zones: DST gaps and repeats flagged, next clock changes, working hours, UTC math. (`UTC = local − offset`) - [Cron Expression Generator & Explainer](https://17x7.com/tools/cron-expression/): Paste a cron expression for plain English, a field-by-field breakdown and next runs in any time zone, or build one. (`*/15 9-17 * * 1-5`) - [JSON Schema Validator](https://17x7.com/tools/json-schema-validator/): Check JSON against a JSON Schema (2020-12, 2019-09, 07, 04): every error as a JSON Pointer, most specific first. (`valid(instance, schema)`) - [JSON Schema Generator](https://17x7.com/tools/json-schema-generator/): Paste sample JSON and get a draft 2020-12 schema with types, required keys and formats, checked against your sample. (`{ "a": 1 } → "integer"`) - [YAML to JSON Converter](https://17x7.com/tools/yaml-to-json/): Convert YAML to JSON and back in your browser, with line-numbered warnings where YAML 1.1 and 1.2 disagree. (`country: NO → false`) - [Robots.txt Tester](https://17x7.com/tools/robots-txt-tester/): Paste a robots.txt and test any URL: verdict, deciding rule and line, plus ten search and AI crawlers at once. (`Allow: /a/b > Disallow: /a`) ## Guides: how the numbers work Formulas explained term by term, with worked examples and the mistakes that cost money. [All guides](https://17x7.com/guides/) - [How Etsy Fees Work in 2026](https://17x7.com/guides/etsy-fees-explained/): 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](https://17x7.com/guides/how-to-price-etsy-products/): 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)](https://17x7.com/guides/amazon-fba-fees-explained/): 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](https://17x7.com/guides/amazon-fba-profit-margin/): 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. - [How to Calculate Roof Pitch, Rafter Length and Shingles](https://17x7.com/guides/how-to-calculate-roof-pitch/): 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](https://17x7.com/guides/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. ## Why 17x7 - **The math is on the page**: Open "Show the math" under any result and you get each step with your numbers substituted. No black boxes, no "estimate may vary" shrug. - **Calculations stay in your browser**: Calculations run locally in JavaScript. There are no accounts, no forms to fill in before you see a result, and no tracking cookies. - **Sources with dates**: Fee tables, code limits and rules of thumb cite where they come from and when we last checked. When a marketplace changes its fees, the page says so. ## Build with 17x7 - [Embed a calculator on your site](https://17x7.com/widgets/): Two lines of HTML, free forever. The only condition: keep the visible "Powered by 17x7" link. - [Give your AI agent a calculator](https://17x7.com/developers/): A keyless JSON API and a remote MCP server with time zone and cron tools — plus every calculator on this site. --- Source: https://17x7.com/ · Last updated: 2026-10-11