Grid Craft is an independent collection of free online calculators. Everything runs in your browser: no signup, no paywall, no email wall. You enter numbers and you get an answer.
Most of the library is practical arithmetic people need mid-task — converting a cake pan, working out how long a brine should ferment, sizing a planter for a balcony, checking pallet or dimensional weight, converting a recipe between cups and grams, or finding the number of days between two dates. Every calculator page has a Formula and Logic section: the equation it uses, the constants and conversion factors behind it, the units, and the rounding applied to the result. The working is there to be checked rather than taken on trust — and if you want to know why a tool works the way it does, ask.
Who runs this site
Ada Kirkwood · Editor, Grid Craft
Ada maintains the calculator library and writes the guides that sit alongside it. She sources each formula, writes it out on the tool page, re-tests it against a worked example before it goes live, and answers the questions and corrections that come in.
Grid Craft is run by one editor rather than a content team. That is deliberate: it means every page has a name attached to it and someone answerable for the numbers.
How the calculators and guides are made
- Start from a task, not a keyword. A tool only gets built when there is a concrete job behind it — scaling a recipe, packing a pallet, spacing bulbs in a bed.
- Write the formula and the logic onto the tool page. Every calculator carries a Formula and Logic section: the equation, the constants and conversion factors it uses, the units, and the rounding applied to the result. Where a value comes from a published standard or a manufacturer specification (pan dimensions, planting depths, container volumes, packaging limits), the page names the source. Where it is plain arithmetic, the working is written out in full so you can reproduce it with a calculator.
- Test it by hand. Before publishing, the calculator is run against a worked example calculated separately, so input handling and rounding are checked rather than assumed.
- State the assumptions. Every tool lists what it assumes — units, rounding, and the cases it does not cover.
- Answer questions about the working. Formula and logic are public, so they can be argued with. If the calculation is unclear, or looks wrong for the case you have in mind, write in — see questions and corrections below.
- Review and re-date. When a referenced table, standard or product spec changes, the tool and its guide are updated and the page’s review date is reset.
What Grid Craft is not
This matters more than anything else on this page, so it is stated plainly:
- Nothing here is advice. The tools run formulas; they do not tell you what to do. You choose the inputs and you own the conclusion.
- No medical, health, legal or financial advice. Pages in those areas are deliberately not part of the library. Where a plain arithmetic cost estimator remains on the site, it is a spreadsheet-style calculation with no recommendation attached, and it is written so you can check the arithmetic yourself.
- No professional relationship. Reading this site does not create an accountant, adviser, attorney, or health professional relationship with anyone, and no page here is written by a licensed practitioner acting in that capacity.
- No credential claims. We do not claim qualifications we do not hold. What we do claim is a process: sourced formulas, worked examples, stated assumptions, and a corrections log.
Questions, corrections and updates
You do not have to be reporting a mistake to write in. Because the formula and the logic are written out on every tool page, they are open to being questioned — by anyone, whether or not they build calculators for a living.
If a calculation is unclear, or you think it is wrong, email [email protected] with the page, the inputs you used, the result you got, and the result you expected. We reply with the working as the page defines it and where each constant comes from.
If the logic itself turns out to be wrong, it is fixed at the source, the page gets a new review date, and the correction stands in place of the old value — we do not quietly remove things and pretend they were never there.
Bulk updates are logged in the same way: when a source table changes and several tools depend on it, every affected page is updated in one pass and re-dated together.
How the site is funded
Grid Craft is self-funded and supported by advertising. Advertisers have no input into which tools are built, what they calculate, or what the guides say, and no advertising agreement affects a formula or a result. Tools stay free, with no account required.
What you will find here
- Cooking and kitchen maths — pan and cake conversions, cooking times, brines and ferments, ingredient ratios, unit conversion
- Home and garden — container watering, planting depths, balcony and plot space, hanging weight, patio sizing
- Work and logistics — pallet and dimensional weight, route and lead times, shift coverage, inventory turnover
- Everyday maths — dates and durations, fractions, aspect and contrast ratios, colour mixing
- Game and tabletop maths — damage, skill allocation, wave and resource estimates
Start from the full calculator library, or read the guides that explain the formulas in detail.
Contact
Questions about how a tool calculates, corrections, and partnership enquiries all go through the contact page or [email protected]. Questions about the working are read first and answered first.
Last reviewed: 16 September 2026.