Driller Math
Pocket references for hydrostatic pressure, mud weight conversions, annular capacity, pump output, strokes↔barrels, displacement, and more. All equations use oilfield units by default.
Reference Equations
Use these with consistent units. Diameters in inches, length in feet, pressure in psi, volume in barrels unless noted.
Hydrostatics & Gradients
Phyd
=
0.052 × MW(ppg) × TVD(ft) (psi)Grad
=
0.052 × MW(ppg) (psi/ft)EMW
=
P(psi) / (0.052 × TVD(ft)) (ppg)Capacities & Displacements
Pipe capacity
=
0.0009714 × ID² (bbl/ft)Annular capacity
=
0.0009714 × (ID² − OD²) (bbl/ft)Pipe displacement*
=
0.0009714 × OD² (bbl/ft) (*outer displacement into fluid)Pumps & Strokes
Vol / stroke
=
(π/4 × LinerID² × StrokeLen) / 231 / 42 (bbl/stk)Vol / min
=
(bbl/stk × SPM × Eff) (bbl/min)Strokes for V
=
V(bbl) / (bbl/stk) (strokes)Circulation & Annular Travel
Lag time
=
AnnularVol(bbl) / Rate(bbl/min) (min)Slug length
=
SlugVol(bbl) / Cap(bbl/ft) (ft)Pressure Windows (quick refs)
MAASP*
≈
LOT(psi) − 0.052 × MW × TVDshoe (*conceptual, use company WCP)KMW
=
MW + SIDPP / (0.052 × TVD) (ppg)Quick Calculators
Fast, offline-friendly calculators for the most common driller math.