Work out the exposure value from aperture and shutter speed, and the scene light value normalised to ISO 100. Enter the shutter as a fraction like 1/125 or a number.
Exposure value combines aperture and shutter: EV = log2(N squared / t). Each whole step is one stop, a doubling or halving of light. The scene light value normalises that to ISO 100, so two settings on different ISOs can be compared. Bright sunlight is about EV 15.
EV is a single number for an exposure: EV = log2(N squared / t), where N is the f-number and t the shutter time in seconds. Equal EVs let the same amount of light in, so f/2.8 at 1/125 and f/4 at 1/60 are both about EV 11.
EV from aperture and shutter does not include ISO. The scene light value normalises it: EV at ISO 100 = EV minus log2(ISO / 100). Raising ISO lets the same aperture and shutter correctly expose a darker scene.
Type it as a fraction like 1/125 or 1/1000, or as a plain number of seconds like 2 or 0.5. The calculator handles both.