When a tensile load is applied into a drillstring, it results in elongation of the drillstring.

The formula to determine pipe elongation is listed below;

**Oilfield unit**

**e = (L x T) ÷ (735,000 x W)**

Where;

e = elongation, inch

L = length of drill string, ft

T = tensile load, lb

W = drill string weight, lb/ft

**Metric (SI) unit**

**e = (L x T) ÷ (26.7 x W)**

Where;

e = elongation, mm

L = length of drill string, metres

T = tensile load, kN

W = drill string weight, kg/m

**Note:** The equations are taken from API RP 7G 16^{th} Edition, August 1998.