Guide
Fun projects still need accurate math
Garden bed layout, aquarium volume, recipe scaling, Lego valuation, and D&D probability guides all exist because a wrong estimate in a hobby project wastes real materials, money, or setup time: too little soil for a raised bed, a recipe scaled without adjusting bake time, or a collectible priced off an incomplete valuation method. Read the formula section first, then apply it to your own project’s exact measurements.
These guides deliberately show the arithmetic rather than just a final number, because hobby quantities usually need adjusting for real-world irregularity (a bed that is not a perfect rectangle, a tank with rounded corners), and seeing the method makes that adjustment possible.
Articles
Where to start in hobbies & leisure utilities
Start with Bowling Handicaps and Darts Checkouts: The League Maths, Soap and Candle Making: Lye, Superfat and How Much Wax, and Homebrew Numbers: ABV, Priming Sugar and Water Salts because they cover the most common questions in this category and each links to the calculator that matches.
36 articles are published in this category so far. Each one follows the same structure: the formula or method, a worked example, a comparison table where relevant, and a direct link to the live calculator.
Context
Rounded measurements produce rounded-off mistakes
Garden and aquarium guides need actual internal measurements, not the manufacturer’s advertised size. A "20-gallon" tank’s advertised volume is the raw dimensional calculation, while the usable water volume is lower once substrate, decor, and the gap below the rim are subtracted, and dosing or stocking guidance is based on that usable figure, not the advertised one.
Recipe scaling guides multiply every ingredient by a yield ratio, but pan size, cooking time, and seasoning do not scale the same way: a doubled cake batter needs a larger pan and a longer bake, not simply double the time, which is exactly the kind of detail the guide calls out explicitly.
Scenarios
Build in an allowance before you buy materials
For any material-quantity guide (soil volume, paint, concrete), calculate the exact figure first, then add the waste allowance the guide recommends before purchasing, since running short mid-project is both more expensive and more disruptive than buying a modest surplus up front.
For probability guides (D&D ability score rolling, dice mechanics), run the comparison the guide sets up (point buy versus rolling, standard array versus custom) against your own group’s house rules rather than the guide’s default assumptions, since a single rule change can shift which method actually produces better outcomes.
Comparison
Collectible valuation is a range, not a price tag
Lego and collectible valuation guides combine a few different signals (price per piece, minifigure rarity tier, theme trends), and each signal alone can be misleading. Price per piece, for instance, is one of the most commonly cited Lego value metrics and one of the least reliable on its own, since it ignores piece complexity, exclusivity, and minifigure content entirely.
Compare a valuation estimate against actual recent sold listings on a resale platform rather than asking prices, since asking prices reflect what a seller hopes for, not what buyers have actually paid recently.
Limits
These are planning estimates, not specifications
None of these guides account for local growing conditions, species-specific animal care requirements, product-specific tolerances, or safety standards. For anything involving structural loads, electrical work, or livestock welfare, official guidance and product instructions take precedence over any figure here.
Valuation outputs in particular are indicative only. Collectible markets move, condition grading is subjective, and a realized sale price depends on venue, timing, and buyer. Use an estimate to decide whether something is worth a professional appraisal, not as a price to trade on directly.