Methodology

The principle

Every result must be reproducible from the inputs on the page. Each calculator is a fixed formula over labeled inputs. There are no hidden scores and no black-box adjustments: the numbers typed, plus the stated defaults, fully determine the outputs. Every calculator page shows its formula, and every calculator ships with automated test cases that fixed inputs must reproduce before publication.

Units and conventions

Dimensions are inches unless labeled otherwise. Money is US dollars. Match flags read 1 for yes and 0 for no. Thresholds follow common US residential practice: 1-3/8 to 1-3/4 in door thickness, 2-1/8 in face bore, 1 in edge bore, and 2-3/8 or 2-3/4 in backset.

Standards referenced

Where grades are discussed, ANSI/BHMA A156 series grades (1 strongest through 3) and UL 437 high-security cylinders are cited as context, never as installation instruction. The manufacturer template and the locally adopted code always govern.

Precision statement

Outputs are screening-grade: good enough to rank options, check a fit, or test a quote. They do not replace the installation template, a physical measurement, or a locksmith survey.

Verification protocol

1. Re-measure thickness, bore, and backset with calipers and tape.
2. Photograph prep, hinges, strike, and clearance.
3. Match the exact manufacturer template for the model being bought.
4. Confirm handing, egress, and power-failure behavior for smart locks.
5. Get parts, labor, and trip fees in writing before authorizing work.

Known limits

No tool here determines code compliance, fire rating, or break-in resistance. Scores rank hardening priorities; they do not certify security. Cluster mailboxes and managed panels require the USPS or property-manager process, not DIY parts.