Methodology

How CalcGrids calculators work — the formulas used, assumptions made, rounding conventions, units, and how we test and correct our calculations.

Formulas and Sources

Each calculator uses a specific, named formula or standard. The formula is documented on the calculator page itself in the “Formula” section. Where multiple established formulas exist (for example, Mifflin-St Jeor and Harris-Benedict for BMR), we use the most widely cited current standard as the primary result and note alternatives.

Formulas are sourced from peer-reviewed literature, established standards bodies, or widely accepted reference sources. We do not invent or modify formulas. Sources are cited on individual calculator pages where applicable.

Rounding

Results are rounded to a practical number of decimal places for the context:

• Calorie and energy values: rounded to the nearest whole number (kcal)
• Currency: 2 decimal places
• Percentages: 2 decimal places unless the context calls for whole numbers
• Distance and unit conversions: 2–4 significant figures depending on the unit
• Financial results (loan payments, interest): 2 decimal places

Intermediate calculations use full floating-point precision; rounding is applied only to the displayed result. This means the worked example on each page may show a slightly different intermediate value than what you would get by rounding at each step.

Units

Calculators that accept unit inputs (metric/imperial) convert internally to a single base unit before calculating, then convert the result back for display. Unit conversion factors are sourced from the International Bureau of Weights and Measures (BIPM) and NIST where applicable.

Assumptions

Many calculators require simplifying assumptions. These are documented on each calculator page. Common assumptions include:

• Financial calculators assume constant interest rates and regular payment intervals
• Health calculators use population-average equations that may not apply to all individuals
• Travel calculators assume constant speed and do not account for stops or traffic
• Construction calculators include a standard waste allowance where noted

Worked Examples

Each calculator page includes a worked example that uses the same formula as the calculator itself. Examples are generated by running the stated inputs through the calculation and rounding the result. If you find a discrepancy between the example and the calculator output for the same inputs, please report it using the contact details below.

Testing

Calculator logic is covered by automated unit tests (Vitest). Tests cover normal inputs, boundary values (zero, minimum, maximum), decimal inputs, and invalid inputs. Tests are run as part of the development process before changes are published.

Reporting Errors

If you believe a formula, result, or worked example is incorrect, please contact us at [email protected] with the calculator name, the inputs you used, the result you received, and the result you expected. We will investigate and correct errors promptly.