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OGtools

Free oilfield converter and field calculator. Drilling, production, reservoir, and gas — built for the rig floor and the office.

Units → Drilling → Production → Gas →
Free forever Works offline No signup Open source
01 — Convert

Oilfield unit converter.

Volume, pressure, temperature, length, mass, flow rate. Edit either side — the other recomputes instantly.

Convert
Pick a category, then a pair of units.

Categories: volume (bbl, gal, m³), pressure (psi, kPa, bar, atm), temperature (°F, °C, K, °R), length, mass, flow rate.

02 — Drilling

Mud, hydrostatics, capacity.

Mud-weight conversions, hydrostatic pressure, pipe and annular volume, equivalent circulating density.

Mud weight
Convert ppg ↔ SG ↔ lb/ft³ ↔ kg/m³ ↔ psi/ft.

Fresh water = 8.3454 ppg = 1.000 SG = 0.4335 psi/ft.

Hydrostatic pressure
Static column pressure at TVD.

P =

P(psi) = MW(ppg) × TVD(ft) × 0.052

Pipe capacity
Capacity per foot and total volume.

Capacity

Volume

bbl/ft = ID² / 1029.4

Annular capacity
Hole vs pipe OD annulus.

Capacity

Volume

bbl/ft = (Dh² − Dp²) / 1029.4

Equivalent circulating density
ECD from MW, APL, and TVD.

ECD

ECD = MW + APL / (0.052 × TVD)

03 — Production

Reservoir & production fluids.

API gravity, gas-oil ratio, and the field correlations engineers reach for first: Standing Bo and gas Bg.

API ↔ specific gravity
Crude oil density on the API scale.

SG = 141.5 / (131.5 + °API)

Gas-oil ratio
Convert between field and metric.

1 scf/STB ≈ 0.1781 Sm³/Sm³

Oil FVF — Standing
Bo at saturation from Rs, gravities, T.

Bo

Bo = 0.972 + 1.47e-4 × F^1.175 ; F = Rs(γg/γo)^0.5 + 1.25 T

Gas FVF
Bg at reservoir T, P.

Bg

Bg = 0.0283 × Z × T(°R) / P(psia)

04 — Gas

Standard gas math.

Volume conversions at standard conditions, Z-factor via Sutton + Brill–Beggs, real-gas density.

Standard volume
scf · Mscf · MMscf · Bcf · Sm³.

Standard conditions: 60 °F, 14.696 psia.

Gas SG ↔ molecular weight
Air = 1.000 reference.

MW = 28.9647 × γg

Z-factor
Brill & Beggs from Sutton pseudo-criticals.

Z

Best for 1.2 ≤ Tpr ≤ 2.4, Ppr ≤ 13.

Real-gas density
ρ at reservoir T, P (Z auto-computed).

ρ

ρ = P · MW / (Z · 10.732 · T(°R))

05 — Preferences

Tune the defaults.

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OG-tools is provided for informational and educational purposes only. Field correlations (Standing Bo, Brill–Beggs Z, etc.) are approximations. Verify against authoritative sources and measured data before any safety-critical use. The authors accept no liability.