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Best Free Electrical & Physics Unit Converters Online

A roundup of the best free electrical and physics unit converters — current, voltage, magnetic field, density, viscosity, moment of inertia, and more.

Reviewed by the thecalcu.com team · Last updated August 4, 2026

Tools reviewed in this article

Electric Current ConverterElectric Potential ConverterMagnetic Field ConverterDensity ConverterViscosity ConverterMoment of Inertia ConverterSound ConverterSurface Tension ConverterAcceleration Converter

Overview

Electrical and physics units are some of the most error-prone conversions on the internet. Mixing up Tesla and Gauss by a factor of 10,000, or poise and pascal-seconds by a factor of 10, produces answers that are wrong but not obviously wrong, which is worse than an answer that's clearly nonsense. This roundup picks the electrical and physics unit converters worth bookmarking, based on unit coverage, precision, and how well they handle the older CGS and imperial units that still show up in datasheets, textbooks, and lab equipment.

What to Look For

A good electrical or physics unit converter covers the full range of units actually used in the field, not just the SI base unit and one metric prefix. It should handle CGS units like Gauss, poise, and erg alongside SI, since a surprising amount of legacy documentation still uses them. Exact standards-based conversion factors matter more than rounded approximations here, since the whole point is avoiding the kind of small error that compounds through a longer calculation. And the tool itself should be fast enough to use mid-calculation without breaking your flow, with no sign-up and no page reload between conversions.

Our Picks

Electric Current Converter

The Electric Current Converter covers amperes across the full metric prefix range (microamps to kiloamps) plus the CGS unit abampere, which appears in older electromagnetic theory texts. It's useful for anything from checking a phone charger's milliamp rating against a power bank's output spec to working through electromagnetism problem sets that mix unit systems.

Electric Potential Converter

The Electric Potential Converter handles volts from microvolts up to megavolts, covering everything from sensor signal levels to transmission-line voltages in one tool. It's particularly handy for electronics work where a datasheet reports a reference voltage in millivolts but your calculation needs volts.

Magnetic Field Converter

The Magnetic Field Converter converts between Tesla (SI) and Gauss (CGS), the two units you'll encounter constantly in electromagnetics, MRI specifications, and geomagnetic field measurements. Given that 1 Tesla equals 10,000 Gauss, this is one of the easiest conversions to get wrong by hand, exactly the kind of gap a purpose-built converter closes.

Density Converter

The Density Converter moves between kg/m³, g/cm³, lb/ft³, and other common density units. It comes up in materials science, fluid mechanics, and everyday tasks like figuring out shipping weight from a material's known density and a container's volume.

Viscosity Converter

The Viscosity Converter handles both dynamic viscosity (pascal-seconds, poise) and kinematic viscosity (centistokes), which matters for anyone working with lubricant or fuel specifications that mix unit conventions depending on the country and industry the spec sheet originated from.

Moment of Inertia Converter

The Moment of Inertia Converter converts between kg·m² (SI) and lb·ft² (common in US mechanical engineering specs). It's relevant for flywheel sizing, motor selection, and rotational dynamics problems where a US-sourced datasheet needs to feed into an SI-based calculation.

Sound Converter

The Sound Converter works with decibel sound pressure level (dB SPL) conversions, useful for acoustics work and for understanding equipment noise specifications that sometimes report levels at different reference distances or weighting curves.

Surface Tension Converter

The Surface Tension Converter converts N/m and related units, relevant to fluid dynamics, coatings, and chemistry applications involving droplet formation, wetting, and capillary behavior.

Acceleration Converter

The Acceleration Converter moves between m/s², g-force, and ft/s², which comes up constantly in automotive and aerospace specs that report braking or launch performance in g-force rather than the SI unit needed for further calculation.

How We Evaluated

Every converter in this roundup is free, requires no sign-up, and runs entirely client-side in the browser, so nothing you enter is transmitted or stored. We checked each one's underlying conversion factors against standards-based references (SI definitions and NIST-published CGS/imperial equivalents) rather than relying on the tool's own claims, and we prioritized converters that include the less-common CGS units alongside SI, since that's where most manual conversion errors happen. For a deeper walkthrough of the electrical units specifically, see our Electrical & Magnetic Units Conversion Guide.

Frequently Asked Questions

Why do electrical units need conversion at all if SI is the global standard?
Even within SI, electrical and physics quantities are routinely expressed at different scales for practical reasons. A car battery is rated in amp-hours while a phone charger is rated in milliamps, and a lab result might report resistivity in ohm-centimetres while a textbook uses ohm-metres. Older instruments and non-US datasheets also still report values in CGS units like Gauss for magnetic field instead of Tesla. Converting correctly avoids errors that compound quickly in downstream calculations.
What's the difference between the Electric Current Converter and just multiplying by 1000?
For simple metric prefix conversions like amps to milliamps, multiplying by 1000 works fine. The [Electric Current Converter](/electric-current-converter/) becomes more useful once you need less common units like abamperes (CGS) or statamperes (esu-CGS), where the conversion factor isn't a round power of ten and is easy to get wrong by hand.
How is density different from specific gravity?
Density is mass per unit volume (kg/m³ in SI), while specific gravity is a dimensionless ratio comparing a substance's density to that of water at 4°C. The [Density Converter](/density-converter/) handles the dimensional unit conversions, kg/m³, g/cm³, lb/ft³, but specific gravity requires an additional division step against water's reference density, which some density calculators build in as an option.
Why does viscosity have two different units, poise and pascal-second?
Pascal-second (Pa·s) is the SI unit for dynamic viscosity, while poise (P) is the older CGS unit still common in older chemistry and materials science literature. One Pa·s equals exactly 10 poise. The [Viscosity Converter](/viscosity-converter/) also handles kinematic viscosity in centistokes, common in lubricant and fuel specifications, which requires dividing by density to convert to or from dynamic viscosity.
What is moment of inertia used for outside of physics class?
Moment of inertia (kg·m²) determines how much torque is needed to achieve a given angular acceleration, which matters directly in mechanical engineering for flywheel design, motor selection, and robotics arm dynamics. The [Moment of Inertia Converter](/moment-of-inertia-converter/) is useful when a datasheet reports it in lb·ft² (common in US engineering specs) and your calculation needs kg·m².
How many decibels is a doubling of sound intensity?
A doubling of sound power corresponds to an increase of approximately 3 dB, while a doubling of perceived loudness, a subjective measure, corresponds to roughly a 10 dB increase, because the decibel scale is logarithmic. The [Sound Converter](/sound-converter/) converts between dB SPL and other acoustic units, but keep in mind dB is already a ratio, so converting it involves logarithmic rather than linear math.
Is surface tension the same as tensile strength?
No. Surface tension (N/m) describes the cohesive force at a liquid's surface that resists external force, relevant to phenomena like droplet formation and capillary action, while tensile strength (measured in pascals, a pressure unit) describes how much stress a solid material can withstand before breaking. The [Surface Tension Converter](/surface-tension-converter/) is specifically for the liquid-surface property, not material strength.
Why does the Magnetic Field Converter list Gauss alongside Tesla?
Tesla is the SI unit for magnetic flux density, but Gauss (the CGS unit) remains common in geophysics, older electronics datasheets, and some medical imaging documentation. One Tesla equals exactly 10,000 Gauss, and the [Magnetic Field Converter](/magnetic-field-converter/) covers both because mixing them up by a factor of 10,000 is a common and costly error.
What's a practical example of needing the Acceleration Converter?
Automotive and aerospace specifications often report acceleration in units like g-force (multiples of standard gravity, 9.80665 m/s²) or feet per second squared, while physics calculations typically use m/s². The [Acceleration Converter](/acceleration-converter/) handles this directly, for example converting a stated 0.8g braking deceleration into 7.84 m/s² for use in a stopping-distance formula.
Are these converters accurate enough for engineering work, or just for quick estimates?
All of these converters use exact, standards-based conversion factors (SI-to-CGS and SI-to-imperial factors defined by international standards bodies), so the arithmetic itself is precise to the number of decimal places shown. For engineering work, always cross-check the specific unit definition your source uses, for example whether a ton of refrigeration or a particular BTU variant matches the standard the converter assumes, since ambiguous unit names cause more errors than the conversion math itself.
Do I need to create an account or pay to use these converters?
No. Every converter listed here runs entirely in your browser, is free with no sign-up required, and works on both desktop and mobile. None of them store or transmit the values you enter.

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GUIDE

Electrical & Magnetic Units: A Practical Conversion Guide