Step back from a campfire and the heat fades fast; step back from a radiation source and the dose fades the same way. For steady exposure the accounting is simple: total dose equals the dose rate multiplied by the time spent, D = rate × t. A dental X-ray delivers its half-millirem in a fraction of a second, while the same dose rate stretched over hours — say, a long flight at altitude — accumulates into something worth tracking. Distance is your other lever, since dose rate itself falls with the square of the distance from the source.

This calculator does the accumulation. Type the dose rate into Variable A — millirem per hour is the everyday US unit — and the exposure time in hours into Variable B; the Result box gives the total dose in millirem. A homeowner in Pennsylvania running a 48-hour radon test at 4 pCi/L, for instance, converts the reading to a dose rate, multiplies by the hours, and compares the Result against the EPA's action guidance. The same multiplication schedules radiology technicians' rotations, plans nuclear plant maintenance shifts, and puts a number on the extra cosmic dose of a cross-country flight.

With the pre-filled defaults — Variable A 10, Variable B 5 — the Radiation Calculator returns Result 50.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.