About smithmetic

Hi — I'm Eric Smith, the developer behind smithmetic. I built it because almost every calculator site I landed on was slow, buried under ads, and stuck in 2008: pop-ups, layout shift, and an answer hidden three scrolls down. I wanted the opposite — type what you need, get the answer instantly, and see exactly how it was worked out.

What smithmetic is

It's a free collection of 100+ calculators and converters across five areas: unit conversion, finance, math, health, and date countdowns. Every page is interactive, works without an account, and shows the formula and a worked example so you can check the math yourself rather than trusting a black box.

Why you can trust the numbers

I don't make up formulas. Conversions use the internationally defined constants (one inch is exactly 2.54 cm; one pound is exactly 0.45359237 kg), and the finance and health tools use standard, widely published formulas — the amortization formula for loans, the BMI definition for body mass index, and so on. Each calculator displays the formula it uses, and the how we calculate page documents the constants and sources in detail. If you ever find a result you think is wrong, tell me and I'll fix it.

How it's built

smithmetic runs at the edge on Cloudflare Workers, so pages respond in tens of milliseconds anywhere in the world. There are no heavy JavaScript frameworks, no cookie banners, and no layout shift — just server-rendered HTML with inline CSS, so the page renders the moment the document arrives, before the small live-calculation script even loads. It also installs as a progressive web app if you want it on your home screen.

A note on advice

The health and finance calculators are for general information and quick estimates. They are not medical, legal, or financial advice — for decisions that matter, check with a qualified professional. The terms and privacy policy cover the details.

The name

smith + arithmetic = smithmetic. I did the math.