1500m time multiplied by 1.08
Or divide a mile time by 1.08 to get a 1500m equivalent.
The ratio if you maintained speed is 1.0727
1.08 accounts for having to slow down a bit to maintain pace another 109 meters.
This ratio works out for most of the top milers.
El G 1.083
Ngeny 1.073 (great mile race)
The ratio is above 1.08 for most because the 1500m is run a lot more often and comparable efforts are not usually given in both events.
3:42.1 1500 converts to a 3:59.9 mile
This ratio has been used by USATF and NCAA for qualifying purposes.