E-Textile Resistance Calculator
Calculate conductive thread and e-textile trace resistance from material type, thread dimensions, stitch count, wash cycles, and operating temperature.
About this calculator
Smart-garment circuits are built from conductive thread instead of copper wire, and this calculator applies the same physics (R = ρL/A — resistance scales with length and inversely with cross-sectional area) using per-material resistivity references at a 0.3mm reference diameter: about 2 ohm/cm for silver-coated nylon, 25 for stainless steel fiber, 100 for carbon-coated thread, and just 0.01 for bare copper. Because resistance is inversely proportional to cross-sectional area, and area scales with diameter squared, a thread diameter different from that 0.3mm reference is corrected by squaring the ratio of reference-to-actual diameter — a thread half as thick has four times the resistance. Each stitch junction where thread meets thread or a component adds its own contact resistance, multiplied by the junction count and added to the thread's own resistance for a base total.
Two degradation factors then multiply that base: wash cycles increase resistance as conductive coatings physically wear (carbon-coated thread degrades fastest at ~3%/wash, silver coating close behind at ~2%/wash, stainless steel and copper barely at all), and operating temperature shifts resistance according to each material's temperature coefficient — metals trend positive (resistance rises with heat) while carbon-coated thread has a negative coefficient, actually dropping resistance as it warms. The tool also reports current and power draw at a typical 3.3V wearable supply, plus a projected resistance after 50 wash cycles for durability planning. These are engineering-reference approximations from published e-textile literature, not measurements of any specific commercial thread — always validate against a multimeter reading before finalizing a garment design.
Inputs
Results
Total resistance (ohm)
218.4
How to Use This Calculator
- Select your conductive thread material (silver-coated nylon, stainless steel, carbon, or copper wire).
- Enter the total thread length (cm), thread diameter (mm), and number of stitch junctions in the circuit.
- Set the contact resistance per stitch (Ω) based on construction quality — typically 0.1–2 Ω.
- Enter wash cycles completed and operating temperature (°C) to account for degradation.
- Review total resistance (Ω), estimated current at 3.3 V, and power dissipation in the outputs.
How the result changes with Thread diameter (mm)
| Thread diameter (mm) | Total resistance (ohm) |
|---|---|
| 0.15 | 842.4 |
| 0.23 | 380.18 |
| 0.45 | 102.84 |
| 0.75 | 43.68 |
What each input means
- Thread material
- Select the thread material
- Thread/trace length (cm)
- Total length of the conductive path in centimeters.
- Thread diameter (mm)
- Diameter of the conductive thread in millimeters.
- Number of stitch junctions
- Number of stitch connection points adding contact resistance.
- Contact resistance per stitch (ohm)
- Electrical contact resistance at each stitch junction.
- Wash cycles completed
- Number of machine wash cycles the garment has undergone.
- Operating temperature (C)
- Temperature during use. Body contact is typically 33-37C.
What each result means
- Total resistance (ohm)
- Total end-to-end resistance including thread, stitches, wash degradation, and temperature effects.
- Thread resistance (ohm)
- Resistance from the conductive thread alone (before stitches, wash, temp).
- Stitch junction resistance (ohm)
- Total resistance added by all stitch contact junctions.
- Resistance per cm (ohm/cm)
- Linear resistance per centimeter for this thread diameter.
- Current at 3.3V (mA)
- Current flow when 3.3V (typical wearable supply) is applied.
- Power at 3.3V (mW)
- Power dissipated as heat at 3.3V supply.
- Wash degradation (%)
- Percentage resistance increase due to washing.
- Resistance after 50 washes (ohm)
- Projected resistance after 50 machine wash cycles.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersThread material = 0, Thread/trace length (cm) = 100, Thread diameter (mm) = 0.3, Number of stitch junctions = 20 = 7 input(s) provided
- Calculate Total resistanceTotal resistance = baseResistance * washFactor * tempFactor218.4 = 218.4
- Calculate Thread resistanceThread resistance = rPerCm * threadLengthCm200 = 200
- Calculate Stitch junction resistanceStitch junction resistance = numStitches * stitchContactResistance10 = 10
Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does halving the thread diameter quadruple the resistance instead of just doubling it?
Resistance is inversely proportional to a conductor's cross-sectional area, and that area grows with diameter squared, not diameter itself. The calculator applies this by squaring the ratio between the 0.3mm reference diameter and your actual thread diameter — so a thread at half the reference diameter (0.15mm) gets a diameter factor of (0.3/0.15)² = 4, quadrupling its per-cm resistance rather than doubling it.
How much does washing actually degrade a silver-coated thread over its lifetime?
Silver-coated nylon is modeled to degrade about 2% per wash cycle, compounding linearly in this model as washCycles times 0.02 added to a multiplier starting at 1. After 50 washes that works out to a wash factor of 1 + 50 × 0.02 = 2.0, meaning the projected resistance after 50 washes is roughly double the base resistance — noticeably faster degradation than stainless steel, which only accumulates about 0.5% per wash.
Why does carbon-coated thread get less resistive as it warms up, while metal threads get more resistive?
The calculator assigns carbon-coated thread a negative temperature coefficient (-0.005 per °C), reflecting the NTC (negative temperature coefficient) behavior real carbon-based conductors exhibit — their resistance drops as temperature rises. Silver, stainless steel, and copper all get positive coefficients instead, since metals' resistance increases with temperature as thermal vibration impedes electron flow, which is the opposite physical behavior.
What do the stitch junctions add to the total resistance, separate from the thread itself?
Each stitch junction — where thread connects to thread or to a component — contributes its own contact resistance value, and the calculator multiplies your specified per-stitch resistance by the number of junctions to get a total stitch resistance. That total is added directly to the thread's own length-based resistance to form the base resistance, before the wash-degradation and temperature multipliers are applied on top.
Related Calculators
The questions that sit next to this one — chosen by subject, including calculators filed under a different category.
Wearable Device Comparison Calculator
Score and compare wearable devices using personalized feature importance weights. Calculate cost-per-point, monthly cost, and value metrics.
WearablesWearable App Development Cost Calculator
Estimate development cost, timeline, and ongoing maintenance for wearable companion apps based on platforms, features, health integrations, and team size.
Textile ScienceThread Count Calculator
Calculate total thread count from warp and weft threads per inch for fabric quality assessment.
Textile ScienceFabric Shrinkage Calculator
Calculate fabric shrinkage percentage and determine pre-cut dimensions to achieve desired finished size after washing.
LaundryWash Formula Calculator
Detergent dosing and cycle settings by load and soil level.
More in Technology & Computing.