Twelve husbandry calculations in one dropdown: aquarium volume in gallons and liters, the one-inch-per-gallon stocking check, heater wattage, substrate pounds, terrarium sizes by species, dog crate dimensions, chicken coop and run square footage, eggs and feed per flock, the cats-plus-one litter rule, hay by percent of body weight, and daily walk time by breed group. Every answer is a published rule of thumb with its formula and caveats shown — confirm the big decisions with a vet, a fish shop, or a care sheet.
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FORMULA USEDPet & Aquarium Calculator
One page of pet math
Pick the question from the dropdown and the form adapts: four fields for a glass box, two for a coop, a select for the breed group. Every result shows the substituted arithmetic beneath the board, and every member carries a margin note naming the rule's origin and limits — because husbandry rules of thumb are starting points, not species law.
The rules at a glance
Tanks: 231 in³ per US gallon; heater at 3–5 W per gallon; gravel near 95 lb per cubic foot (1–1.5 lb/gal for a 1–2 in bed); stocking by the rough 1-inch-of-adult-fish-per-gallon heuristic with modern filtration and bioload caveats. Reptiles: snake floor length + depth ≥ 1.5–2× adult length; gecko minimums of 20 gal and up. Dogs: crate length = dog length + 2–4 in; exercise bands of 30–90+ minutes by breed group. Chickens: 3–4 sq ft coop + 8–10 sq ft run per bird, 0.25 lb feed/day, breed-based lay rates. Horses: hay at 1.5–2.5% of body weight. Cats: one litter box per cat plus one.
Worked example
A 48×13×21 in tank: 13,104 in³ ÷ 231 = about 56.7 US gal (≈ 214.8 L).
That tank's heater band: 56.7 gal × 3–5 W = roughly 170–285 W, two heaters spread the risk.
Six hybrid hens: 6 × 5.5 ≈ 33 eggs a week on about 10.5 lb of feed.
A 24 in dog plus 2–4 in per side lands a 30 in standard crate.
A 1,000 lb horse at maintenance: 2% = 20 lb of hay a day, ≈ 0.3 tons a month.
How to use it
Pick the pet question from the “Which pet question?” dropdown.
Fill the dimensions, counts, or weights that appear — unit switches change the formula inputs.
Read the board, the substituted arithmetic, and the margin note about the rule’s caveats.
Confirm build-or-buy decisions with a vet, aquatics shop, or current care sheet before you commit.
Frequently asked questions
How do I calculate my aquarium’s volume in gallons?
Multiply inside length × width × water depth in inches and divide by 231 — there are exactly 231 cubic inches per US gallon. A 48×13×21 in tank holds about 56.7 gallons (214.8 liters) to the brim; real water lines sit 10–15% lower. The cylinder member does πr²h for round tanks.
Does the one-inch-per-gallon rule actually work?
As a first-pass ceiling, not a promise. It ignores body mass, territory, swimming space, schooling, and how much filtration you run — a 4 in goldfish is not four neon tetras. Use it to sanity-check, then research each species, understock, add fish slowly, and let water test results make the final call.
What size crate does my dog need?
Measure nose to base of tail and floor to shoulder, then add 2–4 inches to each: the dog should stand and turn around but not sleep at one end and soil the other. Match the result to the nearest standard size (24/30/36/42/48 in) and use a divider for puppies.
How much room do chickens really need?
The standard planning numbers are 3–4 sq ft inside the coop and 8–10 sq ft of run per bird — assuming daily access outdoors. Flocks confined through winter need more indoor space, and crowding causes pecking and respiratory trouble long before it looks cramped.
How many litter boxes for two cats?
Three, by the cats-plus-one rule: one box per cat plus a spare, distributed across floors and quiet spots rather than lined up together. Some cats accept fewer with extra-large or self-cleaning boxes and daily scooping, but too few boxes is the first suspect in house-soiling.
How much hay should a horse eat per day?
The forage-first baseline is 1.5–2% of body weight in hay per day — about 15–20 lb for a 1,000 lb horse — with hard keepers and heavy work going up toward 2.5%. Never drop below roughly 1.5% without veterinary guidance, and tune the number with your vet, especially for easy keepers and metabolic cases.