The field calculators · 25 tools · free · works offline
The arithmetic, done — and it still works when the internet doesn't.
Every one of these is a number somebody needs standing in a field with no signal: how big the garden has to be, how much rain that roof gives you, what size wire the pump needs at three hundred feet, how many cords you're short. No account, no ads, nothing sold. Open one, use it, print it.
Works with no connectionHow
Visit this page once, on any connectioncached
Open it later with no internet at allworks
Install it to your phone's home screenworks
Download the whole set as one file for a USB stickdownload
Account required, evernone
Your entries are saved in your own browser and never leave the device.
Growing
What to plant, how much of it, and when — counted from your own frost dates.
01The February PencilHow much ground you actually need to feed the people at your table — the one piece of arithmetic that decides the whole season.02Planting & transplant datesWork the whole schedule backward from your own last frost date — when to start indoors, when to set out, when it comes off.03Last date you can still plant itCounting backward from first frost, with the correction almost nobody applies — days get shorter, and the crop slows down.04Plant count & seed neededBed size and spacing in, plants and seed packets out — so you order once.05Compost C:N mixerGet the carbon-to-nitrogen ratio right and the pile heats itself. Get it wrong and it either sits there or smells like ammonia.06Fertilizer & amendment rateTurn a recommendation in pounds-of-nitrogen-per-acre into how much of the bag in your hand to actually spread.
Water
Catch it, store it, move it, and know how long it lasts.
01Rainwater catchmentWhat a roof actually yields — and the first-flush standpipe that keeps the worst of it out of the tank.02Water storage: how long it lastsTank size against real daily use, including the stock — and what it takes to get through a dry spell.03Irrigation requirement & run timeHow much water the garden actually wants this week, and how long to run the zone to deliver it.04Ram pump outputA pump with two moving parts, running on falling water, forever. This tells you whether your creek can do the job.
Power
Size it on December. Measure the load. Test under load.
01Solar array & battery sizingSize it on December, not on June. This is the calculator that decides whether your system works in the month you need it.02Wire size & voltage dropThe calculator that explains why your pump 300 feet away doesn't start — low-voltage DC runs punish distance brutally.03Generator sizing & fuel burnWhat size you need, how long the fuel lasts, and the test that tells you the truth about it.04Battery runtimeHow long the bank actually carries the load — with the inverter losses people forget.
Food & Storage
The arithmetic that decides whether the winter works.
01The winter arithmeticPeople × days × calories. Run it in October while there's still time to fix the gap, not in January when there isn't.02Equilibrium cure calculatorSalt and cure #1 by percentage of the meat's weight — the method that cannot over-salt, done to the gram.03Fermentation salt & brineSalt by percentage for kraut and pickles — the ratio that lets the right bacteria win.04Canning altitude adjustmentWater boils cooler as you go up. This is the correction — and the line between water bath and pressure canner.05Firewood: cords & heatWhat's actually in that stack, how much heat is in it, and how much you need for the winter.06Freezer & storage spaceHow much freezer you need for the beef, and what it costs to run.
Stock
Feed, water and hay — the numbers that size the barn and the tank.
01Flock feed & egg mathWhat the birds eat, what they lay, what the storage costs, and what an egg really costs you.02Livestock water demandDaily water for the animals — the number that sizes your tank, your pump and your winter worry.03Winter hay needsHow many bales to put up, including the waste nobody budgets for.
Build
Fence, concrete, and the trip to town you only want to make once.
The standing rule
Every calculator here tells you what it can't do.
A number out of a box is only as good as the assumptions behind it, so each of these ends with the assumptions written down and the failure mode named. Size your solar on December. Plant by the soil probe, not the calendar. Test the generator by amps under load, never volts unloaded. And nothing on this site — or from any model anywhere — is a substitute for a tested process when the failure mode is botulism.