About The Useful Site

I built The Useful Site because I was tired of simple questions being made harder than they needed to be.

Sometimes I wanted to know how much paint to buy before setting off for the DIY shop. Sometimes I needed to compare storage sizes, work out the odds in a raffle, or check a figure while supporting a Windows computer. The answers were usually straightforward once the right formula was in front of me.

The problem was finding that formula without first wading through pop-ups, account requests, vague explanations, and pages that seemed more interested in keeping me scrolling than helping me finish the job.

So I started building the sort of website I wanted to use myself: choose a tool, enter the figures, see the answer, and understand how it was reached.

Who is behind the site

My name is Daniel Parish, and I have worked in IT for 36 years. I am based in Milton Keynes.

Most of that has been in support, across a number of employers, but fourteen years of it were in education — and those years shaped this site more than any of the rest. Six of them were spent teaching adult beginners basic computer skills, working with people who had never touched a keyboard. At the other end of the scale, I worked as a Microsoft Certified Trainer, training other Microsoft trainers to teach.

Those two things sound like opposites and are really the same skill: working out what someone already knows, and explaining the rest without either patronising them or losing them. That is exactly what a calculator page has to do. It is why every tool here explains its method rather than simply producing a number, and why the aim is that a page teaches you something even if you never enter a figure.

I hold an HND in computer science and a number of Microsoft qualifications.

The technical background explains why the site contains tools for Windows, storage, networking and backups. It is not limited to technology, though — the same approach applies to calculating paint, planning a garden, comparing borrowing costs or estimating a journey.

The site is written and maintained by me. There is no editorial team behind it, and I would rather say so than imply otherwise.

What is here

The site currently holds:

• 301 calculators, planners and checkers across eleven subjects — technology, finance, health, home and DIY, gardening, food and drink, travel, hobbies, yarn and needlecraft, everyday life and forensic science.
• Long-form guides on subjects that do not reduce to a calculation, where the useful answer is an explanation rather than a number.
• Reference pages setting out how the site is written, tested and corrected.

Every calculation runs in your browser. Nothing you type is transmitted or stored, and there is no account, no login and no calculation history.

How it started

Two problems, a few days apart.

The first was at work. I wanted a quick way to check a recommended Windows page file size from a user's machine, without hunting through documentation while someone waited. It seemed like the sort of thing that ought to exist as a single page you could pull up in a browser.

The second was at home. I wanted to know which vitamin was associated with a particular set of symptoms — and every source I found was organised the wrong way round, listing each vitamin and what it does, leaving me to read through all of them looking for the one that matched. What I wanted was the reverse: describe the symptoms, see which deficiency they point at.

The vitamin checker was the first tool published. The page file calculator is still the one I am most pleased with, because it is the one I actually use.

What I found next is the reason the site kept growing: a surprising number of calculators that seem obvious simply do not exist online. Not obscure ones — ordinary, practical things that plenty of people must want and nobody has built, or that exist only buried in a page carrying more advertising than content.

My test for a new tool is straightforward. If there is a real need for it, if the method can be checked against a published source, and if it can be made genuinely usable, I will research it and build it. If I cannot verify the method, or it would only ever produce a number without teaching anything, it does not get built.

How one person produces this much

It is a fair question, and worth answering directly rather than leaving to inference — particularly as the site is new. I started it in July 2026, and it reached its current size quickly.

The site is static — plain HTML, CSS and a small amount of JavaScript, with no content management system and no database. That makes it fast and cheap to run, and it means pages can be built and checked in bulk rather than one at a time.

I use software to help with the repetitive parts: generating the shared structure of a page, and checking that internal links resolve, that JavaScript parses, that headings run in order, that the tool counts quoted in fifteen different places still agree with each other, and that nothing has quietly broken since the last release. Roughly two dozen automated checks run before anything is published, and each one exists because something went wrong once.

What the software does not do is decide whether a tool is worth having, choose the method, judge whether a source is reliable, or decide what a page should say. Every formula is checked against a published source, worked examples are produced by running the calculator's own code rather than by hand, and every page is read before it goes out.

The test I apply is simple: a page should teach the visitor something useful even if they never press the Calculate button. A page that only produces a number has not earned its place.

The site is not a business and it is not my job. It takes five or six hours of my own time in a typical week, and that is what keeps it maintained — checking figures that move, reworking older pages to the standard the newer ones set, and fixing what gets reported.

How pages are written and checked

Four pages set this out in detail, and they are worth reading if you want to know how much to trust what you find here:

• Editorial policy — how pages are chosen, written, sourced and corrected, including where automated tools are and are not used.
• Research and testing — how a calculation is researched, tested against ordinary and edge cases, and reviewed.
• My promise — the standard the site is working towards, in ten plain commitments you can hold it to.
• References and sources — which sources are used, why, and how they are checked.

In short: UK sources wherever the subject is UK-specific — government departments, the NHS, British Standards, Ofgem, the Food Standards Agency, professional institutions and peer-reviewed work. Estimates are labelled as estimates. Where the evidence is contested, the page says so rather than quietly picking a side. Where a subject needs professional advice, the page says that too.

When something is wrong

Things do go wrong. Formulas get misread, figures go out of date, a source turns out to have been secondary when I thought it was primary, and code breaks in ways that are not visible on the page.

Some recent examples, so this is not an abstraction. A guide to damp quoted timescales for a new housing law taken from press reporting; checking against the government's own publication showed one date was wrong and four legal duties had been left out, including the landlord's obligation to rehouse a tenant at their own expense. On eighteen pages the pound sign was printing after the figure instead of before it. On one page a line of code had ended up inside an advertising tag, where it could never run, so part of the form never initialised.

All of those were found and fixed. I mention them because a site claiming never to be wrong is not being honest with you. What matters is whether mistakes get found and put right, and whether the checks improve so that the same kind of mistake cannot happen twice.

If you spot something, please tell me. A report is most useful with the page name, the figures you entered, the result you got and the result you expected.

Keeping it current

Time-sensitive figures are reviewed on a schedule rather than left to drift. Energy unit rates are updated each time the Ofgem price cap changes. Tax thresholds, allowances and legal timescales are checked when they change, and the page records when it was last reviewed.

Every page shows its review date. If that date looks old for a subject that moves quickly, treat the figures with caution and check the source — which is why every page lists its sources.

Older pages are being reworked subject by subject to meet the standard the newer ones set. The site grew quickly and not all of it is yet where I want it. That work is ongoing rather than finished.

How the site is paid for

The calculators are free to use, and advertising helps cover hosting and maintenance.

An advert does not influence a calculation, change a result, or determine which answer is shown. No advertiser has any say in what is published, and nothing here is sponsored content. Where a page is sceptical about a product or an industry — and several are — that judgement is mine.

I would rather be open about that than pretend a growing website costs nothing to run.