How do you determine how many mm of Hg are equal to 5.3 atm of pressure?

We know that $1 \cdot a t m$ will exert a pressure that forces mercury $760 \cdot m m$ up an evacuated column, i.e. $1 \cdot a t m \equiv 760 \cdot m m \cdot H g$.
A measurement of pressure in $m m \cdot H g$ is useful for measuring the variation in daily atmospheric pressure, or for small pressures, i.e. $0 - 10 \cdot c m$ of the mercury column.
If you try to measure pressures equivalent to $5.3 \cdot a t m$ with a mercury column, you will get mercury all over the lab and floor, where it will inhabit every nook and cranny, waiting for some poor punter (you!) to clean it up, which I can assure you is no easy task,