What it calculates
Enter a resistance value in ohms at a known reference temperature, a target temperature and the temperature coefficient for the material model. The result reports adjusted ohms, ratio and percentage change.
Use a signed coefficient based on resistance at 20°C and appropriate to the actual material and source data. The calculator does not identify whether a supplied coefficient belongs to copper, aluminium, a specific alloy or a particular product.
Method and example
The model is Rtarget = Rreference × [1 + (α ÷ 100) × (Ttarget − Treference)]. The supplied coefficient is based on resistance at 20°C and is treated as constant over the entered interval.
A Canadian trade-learning example gives 0.6508 Ω at 20°C for 76.2 m of aluminium wire (the source's 250 ft converted exactly), with α = 0.39%/°C. At 90°C, the adjusted resistance is 0.8285 Ω. The calculator does not infer wire size or material from those example values.
The correction factor must remain positive, and temperatures must be above absolute zero. These are calculation-domain checks, not a material operating-range approval. The model retains full precision and displays four decimals or scientific notation.
Limits and interpretation
This is a linear temperature model. It does not account for conductor construction, skin effect, inductive reactance, joints, terminations, installation heat transfer, short-circuit duty, temperature rating or changes in material properties outside the model range.
The adjusted resistance can support a separately defined voltage-drop or loss calculation when its length and resistance basis match that calculation. It does not replace a listed product table or a reviewed installation method.
No ampacity, conductor selection, breaker choice, thermal limit or Canadian code result is provided.
Common questions
Why does the calculator ask for a coefficient?
Resistance changes depend on the material model. Supplying the coefficient keeps the calculation explicit and avoids silently assuming a material or product.
Can I use a 25°C table value and a 75°C target?
Yes, when the coefficient based on 20°C and its model range are appropriate to the same material and resistance value. Confirm the source's temperature reference and units first.
Does the result prove a conductor is safe?
No. Resistance is only one input to circuit performance. Installation conditions, ampacity, terminations, protection and adopted requirements need separate reviewed data.
Related tools
Sources
Industry Training Authority, Construction Electrician Apprenticeship Program, Level 1, Learning Guide D-1: Use Electrical Circuit Concepts, Learning Task 18, “Temperature effects on resistance,” printed pages 133–135 (Version 1, January 2011). It defines the coefficient from resistance at 20°C and provides the resistance-change equation and an aluminium-wire example. This educational source is used for the generic physical method only; no provincial code rule or installation approval is claimed.
Sources and scope checked November 10, 2026. Report a problem or suggest a source; inputs are not attached automatically.