About

What LockCalculator.com is

LockCalculator.com publishes free screening calculators for residential door locks in the United States: measuring existing door preparation, checking smart-lock fit, pricing rekeying against replacement, planning keys and access, and budgeting parts and labor. Every calculator states its inputs, shows its formula, and ships with machine-checked test cases that fixed inputs must reproduce before publication. How calculations are built and checked is documented on the methodology page.

Who it is for

Homeowners replacing a lock, landlords turning over a unit, property managers running key control across several doors, and anyone comparing a DIY job against a locksmith quote. The tools assume common US residential preparation — 1-3/8 to 1-3/4 inch door thickness, 2-1/8 inch face bore, 1 inch edge bore, and 2-3/8 or 2-3/4 inch backset — and say so wherever a threshold matters.

What it is not

This site is not a locksmith and does not sell hardware, dispatch technicians, or certify security. Calculator results are screening outputs: good enough to rank options, check a fit, or test a quote. They do not replace the manufacturer installation template, a physical measurement, fire-egress requirements, or the locally adopted code. Confirm the exact lock model, photograph the preparation, get work quotes in writing, and check local rules before buying or drilling. The full boundary is stated in the disclosure.

How the site is organized

Calculators are grouped by job: door measurement, smart locks, lock changes and keying, cost and scheduling, security hardening, and specialty checks such as mailbox locks. Each calculator page carries a plain-language guide, a verify-before-you-buy checklist, related calculators for the next step, and related articles that go deeper. The guides index collects every article in one place.

Corrections

Thresholds, prices, and product behavior change. If a calculation disagrees with a manufacturer template or a metered result, use the problem-feedback form on the calculator page and include the inputs entered so the result can be reproduced. Corrections ship with the test case that proves them.