Drilling Ton-Mile is the work of drilling line that is commonly measured as the cumulative of the load lifted in tons and the distance lifted or lowered in miles. When the predetermined ton-mile limit is reached, drilling contractors will perform slip and cut drilling line to prevent drilling line fatigue.
When drilling line is spooled on and off a drawworks drum during operation as drilling a well, running casing, coring, etc.The drilling line get worn out; therefore, drilling contractors must cut old section and replace with new section of drilling line at specific period based on ton mile calculation.
The most worn area is the end of drilling line where is constantly spooled over the draw works drum. A section of drilling line, typically around 100 ft, is cut then the drilling line is re-attached to the draw works drum and the amount cut off is spooled back on the drum. This operation is called “slip and cut drilling line”.
Note: Ton-mile is the important figure that must be recorded correctly. However, the most important is to visually inspect drilling line all time to see if there is any worn out wire. If you see the worn out line, you need to cut the drilling line even though the drilling line does not reach ton-mile limit yet.
All types of ton-mile service should be calculated and recorded in order to obtain a true picture of the total service received from the rotary drilling line. There are several types of ton miles as follows;
1. Round trip ton-miles
2. Drilling or “connection” ton-miles
3. Coring ton-miles
4. Ton-miles setting casing
5. Short-trip ton-miles
Ref book: 
Formulas and Calculations for Drilling, Production and Workover, Second Edition
I need to have a copy Round trip ton-miles calculation. How do I go about it?
Here we go =>
How do you know when to slip and cut drilline if no wear is visible. How many tonmile between cuts and how to figure how much should be cut. Please explain.
Amie,
Each drilling line has a recommended ton-mile for cutting.
Can you give links with table which has recommended ton miles for different line sizes
Ton-mile figures should be found in manufacturing technical data. It depends on which models/brands that you use on the rig. I cannot specifically inform you about it.
How do you know jarring tonmile?
There is no calculation regarding jarring tonmile.
At what time or part of the 12 hour shift do you calculate ton miles ? or is it 24 hours midnight to midnight ?
Tone mile should update every shift so you will not lose the record. TM is a work done on the drilling line. Basically, it depends on load you work and how far you work with the load.