signal-to-noise ratio (SNR; S/N)

jam to signal ratio (J/S ratio)

signal-to-interference-plus-noise ratio (SINR)

reduction ratio / gear ratio

Voltage Standing Wave Ratio (VSWR) / voltage standing-wave ratio

Signal Kit / MK-79 (illumination signal kit)

aspect ratio

fighter-to-administrative personnel ratio

high expansion-ratio

mass ratio

power-to-weight ratio

thrust-to-weight ratio

damping ratio

attenuation ratio

base pressure ratio

weight-horsepower ratio

weight-strength ratio

depression ratio

explosion ratio

infantry-armor ratio

forward gear ratio

fuel-air ratio

fuselage fineness ratio

compression ratio

engine pressure ratio (EPR)

excess air ratio

fuel hydrogen / carbon ratio

hub-tip ratio

mixture ratio

pressure ratio

pressure ratio controller

space-chord ratio (of turbomachine cascade)

stage reaction ratio