# Weight Converter

> Weight converter: pounds, kilograms, ounces, grams, and stones. Free weight converter with the formula shown - runs entirely in your browser, no signup.

- **Canonical URL:** https://boringtoolskit.com/weight-converter/
- **Category:** Converters
- **Evidence level:** authored-methodology
- **Reviewed:** 2026-09-20
- **Last verified:** 2026-10-12
- **Privacy:** Inputs and results stay in this browser unless the page clearly labels an external request.

## How it works

Value x (kilograms per source unit) / (kilograms per target unit), using exact factors: pound 0.45359237, ounce 0.028349523, stone 6.35029, tonne 1000.

## Worked example

1 pound = 0.4536 kilogram · 1 stone = 6.35 kilogram · 1 ounce = 28.35 gram

## Assumptions

- Inputs are treated as exact decimal values.
- Standard (not historical or survey) unit definitions are used.
- The calculation uses the factors at the precision shown in the formula panel; rounding beyond that is display-only and adds no accuracy.

## Common questions

### Why convert through kilogram instead of directly?

Routing every unit through a single base (kilogram) means each unit needs only one exact factor against the standard, and any pair combines cleanly. Direct pair factors drift apart over time in hand-maintained tables; a base-unit graph cannot.

### Where do these exact factors come from?

From published standards (NIST: SI SP 330 mass definitions). Units like the inch are defined exactly (1 in = 2.54 cm since 1959), so conversions between standard units are exact, not approximate.

### How many decimal places should I trust?

The math is exact to the precision shown. The practical limit is your input: a tape measure is only good to ~1 mm and a kitchen scale to ~1 g, so 3–4 significant figures already exceeds the measurement's own accuracy.

## Sources

- [SI SP 330 mass definitions](https://www.nist.gov/pml/special-publication-330)

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