Relay Sizing Calculator

Size automotive relays based on load current, coil voltage, duty cycle, and contact rating with derating for inductive loads.

Input Parameters

Results

--
Min Contact Rating
A
--
Coil Current Draw
mA
--
Contact Power Diss.
W
--
Est. Life Cycles
Note: Inductive loads cause arcing on relay contacts. Use snubber diodes across relay coils. ISO 7588 covers automotive relay standards.

Reference

Min Contact Rating = Load Current / Derating Factor Derating: Resistive=1.0, Motor=0.5, Lamp=0.33, Cap=0.4 Coil Draw = V_coil / R_coil (typ. 85 ohms) Contact Power = I² × R_contact Life = Base_cycles × Derating × Duty_factor