Estimate how much pipe is free above a stuck point from a measured stretch and the differential pull that caused it.
When pipe gets stuck, the free point is the depth where it stops being free to move — everything above stretches when you pull, everything below is held fast. Knowing it tells you where to back off, set a jar, or run a string shot. You find it by pulling a known extra load, measuring how far the blocks travel (the stretch), and working back to how much pipe must be free to have stretched that much.
This is the same elastic relationship as the stretch calculator, solved the other way round — stretch in, free length out.
Stretch in inches, area is steel cross-section in in² (or pipe weight in lb/ft divided by 3.4), E is 30 × 10⁶ psi for steel, and pull is the differential load in lbs. The ×12 keeps the units in feet.
An estimate. Assumes uniform pipe, purely elastic stretch, and that all the measured travel is genuine pipe stretch (not slack, blocks, or deviation drag). Deviated and tapered strings reduce accuracy.
A 30 in stretch from a 50,000 lb differential pull on pipe with 5.275 in² of steel: free point = (30 × 5.275 × 30,000,000) / (50,000 × 12) ≈ 7,919 ft of free pipe.
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