Download Time Calculator

The formula this calculator uses

time = size in megabits / speed in megabits per second

size

File size, converted to megabits by multiplying gigabytes by 8000

speed

Connection speed in megabits per second

t

Transfer time in seconds, then converted to minutes

eff

Fraction of the advertised speed actually achieved

How to check the result by hand

1. 1

   Convert the file size to megabits

   Multiply the gigabytes by 8000. A 20 gigabyte file becomes 160000 megabits, because a gigabyte is a thousand megabytes and each megabyte is eight megabits.

2. 2

   Keep the connection speed in megabits per second

   The advertised figure is already in the right unit, so no conversion is needed at this stage. Converting it to megabytes now would double-count the factor of eight.

3. 3

   Divide to get the theoretical seconds

   160000 megabits on a 100 megabit line is 1600 seconds. This is a floor, not a prediction, because it assumes every bit arrives at the full advertised rate.

4. 4

   Multiply the speed by the efficiency

   Ninety-two percent of 100 megabits per second is 92 megabits per second. Using this effective rate in place of the advertised one gives the realistic transfer time.

5. 5

   Convert the seconds to minutes and check the size

   Divide by sixty to get 28.9855072464 minutes. Cross-check by noting that the connection moves 12.5 megabytes per second, which at that rate delivers the file in roughly half an hour.