# Energy Converter > Energy converter that switches between joules, calories, kWh, BTU, foot-pounds, electronvolts, and more instantly. Free, runs in your browser, no signup. - **Canonical URL:** https://boringtoolskit.com/energy-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 Energy = value x (joules per source unit), then joules / (joules per target unit). Factors: 1 kWh = 3600000 J, 1 cal = 4.184 J, 1 kcal = 4184 J, 1 Wh = 3600 J, 1 BTU = 1055.06 J. ## Worked example 1 BTU = 1.055 kilojoule ยท 1 kilocalorie = 4.184 kilojoule ## 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 joule instead of directly? Routing every unit through a single base (joule) 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: SP 811 energy conversions). Units like the inch are defined exactly (1 in = 2.54 cm since 1959), so conversions between standard units are exact, not approximate. ### How precise is the converted energy value? The conversion applies the standard factors shown in the formula panel. The practical limit is your input: the result only regroups the number you entered, so digits beyond your original reading do not add accuracy. Note that 1 kWh = 3.6 MJ exactly, while thermal and electrical conversions carry their own efficiency assumptions. ## Sources - [SP 811 energy conversions](https://www.nist.gov/pml/special-publication-811) --- *Local planning estimate. Verify current terms, rates, and policies before acting.*