Approximate conversion of Radians to USSR milliradians
Multiply by 955 and you're within a whisker. The Soviet artillery mil splits a circle into 6,000, so one radian is 6,000 ÷ 2π, about 954.93 mils.
That makes 0.5 rad roughly 477 mils and 2 rad roughly 1,910. Treating them as true milliradians, 1,000 to the radian, puts you nearly 5% out – fine for a sketch, not for aiming anything.
NATO mils are different again, at 6,400 to the circle, so check which kind a map or sight uses before trusting a number.
About Radians
The radian is the SI unit of angle. A full circle is 2π (about 6.28) radians, against 360 degrees.
The concept of radians is based on the relationship between the length of an arc and the radius of a circle. One radian is defined as the angle subtended by an arc that is equal in length to the radius of the circle. In other words, if we were to take a circle with a radius of 1 unit and measure an arc along its circumference that is also 1 unit long, the angle formed at the center of the circle would be 1 radian.
A radian is a ratio of two lengths, arc over radius, so it carries no units of its own and drops out of physics formulas – speed = radius × angular velocity works directly when the angle is in radians.
About USSR milliradians
The USSR mil was the angle unit of Soviet artillery. It is a rounded version of the milliradian, within a few percent of one thousandth of a radian.
Soviet artillery used the mil in its sights and for estimating range: a target of known width that covers a measured number of mils gives the distance.
Like the other mils it is a military convention rather than an SI unit – each army chose a convenient number of divisions for the circle, so check which mil a figure refers to.
There are 6,000 USSR milliradians to a full circle.