Quick Reference

Drilling Formulas Cheat Sheet

The eight formulas that come up most on the rig floor — well control and basic string math — in one place. This is a reference for which formula applies and what it needs — for the actual number, use the linked calculator with your real figures.

Every formula below is reviewed for accuracy by Jabin Travis, IADC WellSharp-certified driller, same as the calculators themselves.

Hydrostatic Pressure
HP (psi) = 0.052 × MW (ppg) × TVD (ft)
The static mud column pressure at a given depth. Run it: Hydrostatic Pressure Calculator.
Kill Mud Weight
KMW = OMW + (SIDPP ÷ (0.052 × TVD))
The mud weight needed to balance the well after a kick, from shut-in drill pipe pressure. Run it: Kill Sheet Calculator.
Maximum Allowable Annular Surface Pressure
MAASP = LOT/FIT Pressure + [(LOT/FIT MW − Current MW) × 0.052 × Shoe TVD]
The ceiling on surface pressure before the shoe takes fluid. Run it: MAASP Calculator.
Kick Tolerance
KT = [MAASP − (Influx Height × MW × 0.052)] ÷ (0.052 × Shoe TVD)
How much kick the well can take before MAASP is exceeded. Run it: Kick Tolerance Calculator.
Equivalent Circulating Density
ECD = MW + (Annular Friction Loss ÷ 0.052 ÷ TVD)
The effective mud weight while circulating, once friction pressure is added. Run it: ECD Calculator.
Trip Margin / Safety Factor
TM/SF = Base Mud Weight + [Safety Margin ÷ (0.052 × TVD)]
Extra mud weight carried to cover swab pressure while tripping. Run it: Trip Margin Calculator.
Buoyancy Factor
BF = 1 − (Fluid Weight (ppg) ÷ 65.5)
The fraction of a string's air weight it actually hangs as once submerged in fluid. Run it: Buoyancy & Tubular Weight Calculator.
Capacity & Displacement
Capacity (bbl/ft) = ID² ÷ 1029.4
Displacement (bbl/ft) = (OD² − ID²) ÷ 1029.4
Volume per foot inside the pipe, and volume per foot the pipe itself displaces. Run it: Drill Pipe Tally Calculator.

For the full concept behind these — how pore pressure, fracture pressure, and mud weight window all tie together — see the hydrostatic pressure reference page. For the complete list of tools, back to all drilling calculators.

FAQ

Frequently Asked Questions

No — it's a quick reference for which formula applies and what it needs, not a calculator. Each one links to the real, interactive calculator on this site where you actually enter your numbers and get a result.

Because a worked example uses someone else's numbers, not yours. The calculators are free, show their formulas openly, and take seconds to run with your actual figures — that's a safer habit to build than memorizing a sample answer.