Free tools · no signup
Calculators for the jobs you do by hand
Grid Craft is a small, independent library of free calculators — pan conversions and cooking times, planting and watering maths, packaging and route arithmetic, plus the everyday date and ratio tools. Every calculator page carries a Formula and Logic section: the equation it uses, the constants, the units, and how it rounds. If the working looks wrong to you, write in and we will go through it.
Start with a task
A selection from the main areas of the library, grouped by the task you are on. The full set lives in the calculator index.
Kitchen & cooking
Conversions and timings you reach for while actually cooking.
Home & garden
Space, depth and watering maths for beds, pots and balconies.
Work & logistics
Packaging, routing and coverage arithmetic for small operations.
Everyday maths
Dates, durations and proportions — the plain-number tools.
Guides that show the maths
Longer walkthroughs for the questions people ask most, written so the reasoning is visible rather than hidden behind a result box.
How long to boil eggs: the tested timer chart
Soft, jammy and hard yolks by size and altitude, with the peel-ease notes that most charts leave out.
Read the guide →How to calculate container plant watering
The 1/2/3:2:1 method for working out how much water a pot actually needs, plus a scale check.
Read the guide →How to convert cooking units without an app
Why a cup is not a fixed weight, and the mental maths that gets you close enough to cook with.
Read the guide →Who writes Grid Craft
Ada Kirkwood
Editor · writes and maintains the calculator library
Ada sources each formula, writes it out on the tool page, tests it against a worked example before it goes live, and answers the questions and corrections that come in. Grid Craft is not a content farm and not a clinic, firm or brokerage: the site publishes arithmetic, and where a number depends on a published standard or a manufacturer specification, the page says where it came from.
How every tool is checked
- Formula and Logic on the pageEvery calculator sets out the equation it uses, the constants behind it, the units and the rounding — in a section headed Formula and Logic, so the arithmetic can be checked line by line.
- Sourced, not inventedWhere a number comes from a public standard, a published table or a manufacturer specification, the page names it. Where it is plain arithmetic, the equation is written out in full.
- Hand-testedEach calculator is run against a separately worked example before publishing, so input handling, units and rounding are checked rather than assumed.
- Assumptions statedEvery tool lists what it assumes, what it does not cover, and that results depend entirely on what you enter.
- Questions answeredIf a calculation is wrong — or you simply want to know why it works that way — email the inputs you used and the result you expected. We show the working or fix the tool.
Grid Craft does not publish medical, legal or financial advice, and no page here is written by a licensed professional acting in that capacity. The tools are arithmetic only — you choose the inputs and you own the conclusion. Every formula is open to inspection on the page it belongs to, and every question about how a figure is arrived at gets an answer: [email protected].