Resistance Converter
Convert ohms, milliohms, kilohms and megohms, with conductance in siemens shown alongside — and the resistance of an object kept distinct from the resistivity of a material.
Resistance Converter
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- No temperature correction is applied, though real conductor resistance rises roughly 0.4% per degree Celsius for copper.
- The Ohm's law card assumes a purely resistive, linear component and ignores reactance and non-linearity.
- This converts units; it does not size resistors for power dissipation or calculate network equivalents beyond the two-component illustration.
In short: Resistance converts through the ohm, one volt per ampere. The SI prefixes are exact powers of ten, so 1 kΩ is 1,000 Ω and 1 MΩ is one million. Its reciprocal is conductance in siemens. Keep two ideas apart: resistance belongs to a specific object and depends on its length and cross-section, while resistivity belongs to the material itself.
Formula
Each factor is the number of ohms in one of that unit. The SI prefixes are exact powers of ten. Conductance in siemens is the exact reciprocal of resistance in ohms.
Worked Example
- Identify the source factor. One ohm is 1.
- Convert to the SI unit. 4,700 × 1 = 4,700 Ω.
- Identify the target factor. One kilohm is 1,000 Ω.
- Divide. 4,700 ÷ 1,000 = 4.7 kΩ.
- Take the reciprocal for conductance. 1 ÷ 4,700 = 212.77 µS.
Why the same copper gives different resistances. Resistance follows R = ρL/A. Copper's resistivity is about 1.724 × 10−8 Ω·m, so 100 m of 2.5 mm² cable is 0.69 Ω while 100 m of 10 mm² cable is only 0.17 Ω. At 16 A the thin cable drops about 11 V one way, or 22 V on the round trip — nearly a tenth of a 230 V supply lost as heat. Nothing about the material changed; only the geometry did.
Strengths & Limits Of This Model
Where this engine is strong
- Shows conductance in siemens alongside every result, keeping the reciprocal relationship visible.
- Refuses negative resistance rather than formatting a meaningless figure.
- States the R = ρL/A distinction explicitly instead of conflating resistance with resistivity.
Where it stops
- No temperature coefficient handling.
- Does not model reactance or impedance.
- Not a resistor power-rating or network-solving tool.
Practical Use Cases
Electronics design and component selection
Resistor values span microhms to gigohms and datasheets mix Ω, kΩ and MΩ freely, often within a single table.
Cable and busbar calculations
Conductor resistance in milliohms per metre drives voltage drop and resistive loss, both of which scale with the square of current.
Insulation and safety testing
Insulation resistance is measured in megohms and gigohms, and acceptance criteria are written in those units.
Sensor and measurement circuits
Thermistors, RTDs and strain gauges are all resistance-based sensors — pair with the Voltage Converter when working through a bridge circuit output.
Methodology & Editorial Standards
All conversions route through the ohm, the SI unit of electrical resistance, defined as one volt per ampere. The SI prefixes are exact powers of ten. The statohm and abohm belong to the CGS electrostatic and electromagnetic systems respectively; the statohm factor is derived from the exact speed of light rather than transcribed. Conductance in siemens is reported as the exact reciprocal. The engine refuses negative input, since a passive resistance cannot be negative; the negative differential resistance shown by some active devices is a slope on a characteristic curve rather than a component value and is out of scope. The Ohm's law and series-parallel cards are labelled cross-checks, not the purpose of the page, and resistance is kept explicitly distinct from resistivity, which is a material property with its own converter. Resistance is also temperature-dependent, rising roughly 0.4% per degree Celsius for copper, and this converter applies no temperature correction. All conversion factors are exact by definition under the International System of Units, or exact by international agreement where the unit is defined by treaty. Values are held at full IEEE-754 double precision internally and rounded only for display, so chained conversions do not accumulate drift.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Resistance Converter — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How many ohms are in a kilohm?
Exactly 1,000, and a megohm is exactly one million ohms. All SI prefixes are exact powers of ten, so these conversions carry no uncertainty. Note the spelling conventions: megohm and kilohm drop the second o, though kilohm is also written kiloohm in some standards.
What is the difference between resistance and resistivity?
Resistance is a property of a particular object and is measured in ohms; cut the wire in half and its resistance halves. Resistivity is a property of the material and is measured in ohm-metres; it does not change when you cut the wire. They are related by R = ρL/A, where L is length and A is cross-sectional area.
What is conductance and how does it relate to resistance?
Conductance is the reciprocal of resistance, measured in siemens. A 50 Ω resistor has a conductance of 0.02 S, or 20 mS. Conductance is more convenient for parallel networks, because parallel conductances simply add, whereas parallel resistances have to be combined as reciprocals.
Can resistance be negative?
Not for a passive component. Some active devices, such as tunnel diodes and certain gas discharge circuits, show negative differential resistance over part of their characteristic, meaning current falls as voltage rises in that region. That is a slope on a curve rather than a component value, and this converter refuses negative input rather than returning a meaningless result.
Why do resistors have odd values like 4.7 kΩ?
Because standard values follow the E-series, which are geometric progressions chosen so that consecutive values differ by roughly the component tolerance. The E12 series gives twelve values per decade at about 10% spacing, which is where 4.7, 6.8 and 8.2 come from. The values look arbitrary but are logarithmically even.
Does resistance change with temperature?
Yes, substantially. Copper's resistance rises about 0.4% per degree Celsius, so a winding at 100 °C has noticeably more resistance than the same winding cold; this is how motor temperature is often inferred. Thermistors are designed to exaggerate the effect, while precision resistors use alloys chosen to minimise it. This converter applies no temperature correction.
How do I calculate the resistance of a length of cable?
Use R = ρL/A. For copper, take resistivity as about 1.724 × 10⁻⁸ Ω·m, so 100 metres of 2.5 mm² cable gives roughly 0.69 Ω. Remember to count both conductors for a round trip, which doubles the drop, and note that stranded cable has slightly more resistance than its nominal cross-section suggests.
What is a statohm?
The resistance unit of the electrostatic CGS system, equal to about 8.9876 × 10¹¹ ohms. The number is the square of the speed of light in centimetres per second divided by 10¹⁰, which is why it is so large and so oddly specific. Along with the abohm it appears only in older physics literature.