Small tools for real questions.
The sums people do on the back of an envelope before they buy wood, leather, arrows or a tank, done properly and explained. Everything runs on the page; nothing is sent anywhere.
Janka hardness and weight of 34 woods and 3 sheet goods, sortable, with what each is good for.
Calculator · Rock collecting, Collecting vintage tackle and more Shelf sag calculatorHow far a shelf sags under a load, and the thickness or span that keeps it flat.
Calculator · Whittling, Pyrography Board foot calculatorBoard feet and cost of a board or a stack, from thickness in quarters, width and length.
Converter · Leathercraft, Bookbinding Leather thickness converterOunces, millimetres and inches, with what each leather weight is used for.
Calculator · Leathercraft, Bookbinding Saddle stitch calculatorStitches and thread length for a hand-sewn seam, from its length and spacing.
Calculator · Traditional archery, Arrow fletching Arrow weight and FOCGPP, FOC and a draw length estimate for a traditional bow.
Calculator · Backpacking, Shed hunting and more Pack weight builderBase weight and total pack weight from a gear list you keep in your browser.
Converter · Fly fishing, Tenkara and more Tippet size finderWhich tippet for which fly, with diameters and strengths for 0X to 8X.
Calculator · Terrariums, Shrimp tank and more Tank and pot volumeGallons, liters, full weight and the soil or substrate for any tank, pot or tray.
Calculator · Natural dyeing, Basket weaving Mordant calculatorGrams of alum, tannin and iron for the weight of fiber you are dyeing.
Calculator · every hobby Cost per hour of hobbyAny hobby here, at your hours per week: the cost per hour in year one and after.
Calculator · Film photography Sunny 16 exposureAperture and shutter for any film speed and light, by the sunny 16 rule.
Converter · Knitting, Crochet Yarn weights and needle sizesYarn weight 0 to 7 to needles, hooks and gauge; millimetres to US sizes.
Calculator · Knitting, Crochet Yarn amount from a swatchGrams, yards and skeins for a project, from the weight of your own swatch.
Calculator · Cross-stitch, Embroidery Cross-stitch fabric sizeDesign size and fabric to cut from the stitch count, for Aida or evenweave over two.
Calculator · Sourdough baking Baker's percentagesTrue hydration with the starter counted, salt and starter shares, and scaling.
Calculator · Pottery (hand-building) Clay shrinkage and firing costWet size for a finished size, and studio firing fees by the cubic inch.
Calculator · Running, Trail running Running pacePace per km and per mile, finish time and splits for any distance.
Calculator · Backyard chickens Chicken coop sizeCoop floor, roosting pole and nest boxes for your number of hens.
Calculator · Beekeeping Sugar syrup for beesSugar and water for 2:1, 1:1 or any syrup, by weight or by volume.
Where the numbers come from
Wood figures are from the USDA Forest Products Laboratory Wood Handbook. Beam sag uses the standard formulas for a simply supported or fixed beam. Leather, thread, tippet and arrow rules are the ones the trades use; where makers disagree, the page says so and gives the range. The cost per hour tool uses the kit and monthly costs from each hobby's card, the same numbers explained on how we get the numbers.
These are estimates for choosing and buying, not engineering advice. A shelf that holds a library, a bow that is shot with a light arrow, or a tank on an upstairs floor deserve a second opinion from someone who can see the thing.