The DIN 43760 standardised temperature coefficient of platinum wire is: α = 0.00385. For a resistance of 100 ohms at 0 °C, this corresponds to + 0.385 ohm per °C (European α). α is therefore the average slope from 0°C to 100°C $$ \alpha = \frac{{{R_{100}} – {R_0}}}{{ {R_0} \times 100^\circ C.}} $$. There is a wide range of RTDs which have different α coefficients and ohm values at 0°C detailed in their technical properties. The most commonly used RTD is that with an α coefficient of 0.00385 and ohm value at 0°C of 100 Ω. It is known as Pt100.

Values of some RTDs
R at 0°C (Ω)α (Ω/Ω/°C)Average sensitivity (Ω/°C)
25.50.003920.1
1000.003920.392
1000.003910.391
1000.003850.385
2000.003850.770
4700.003921.845
5000.003921.963
5000.003911.955
5000.003851.925
10000.003853.850
10000.003753.750
100000.0038538.50
International standards DIN 43760 (IEC 751, BS-1904, JIS C1604)
ParameterClass AClass B
R0100Ω ±0,06%100Ω ±0,12%
Alpha, α0,00385 ±0,0000630,00385 ±0,000063
Range-200°C to 650°C-200°c to 850°C
Res, RT±(.06+.0008|T|-2e-7T2)±(.12+.0019|T|-6e-7T2)
Temp, T±(0.3+0.002|T|)°C±(0.3+0.005|T|)°C