Annular Capacity Calculator
Calculate annular capacity and volume in bbl/ft, gal/ft, ft/bbl, liters, and stepped multi-interval wells.
Annular capacity between casing and pipe
Use casing ID or hole diameter—not casing OD—plus tubing or drill-pipe OD. See capacity per foot, total barrels, gallons, liters, fluid weight, and stepped intervals.
Edit the annulus
Stepped or multi-interval well
Add sections with different casing IDs, pipe ODs, or lengths.
How annular capacity is calculated
The outer value is the hole diameter or casing inside diameter. The inner value is the outside diameter of drill pipe, tubing, or inner casing. The calculator subtracts the inner circular area from the outer circular area and multiplies by interval length.
In US oilfield units, the exact geometric conversion uses 9,702 cubic inches per 42-US-gallon barrel. The familiar rounded field form is approximately (outer ID² − inner OD²) ÷ 1,029.4 for bbl/ft.
Need volume inside the tubing rather than around it? Use the Tubing Capacity Calculator.
Planning estimate only. The model assumes concentric, constant-diameter cylinders. Verify actual casing ID, drift and open-hole caliper, and account for washout, eccentricity, tool joints, couplings, cable, packers, scale, and other displaced equipment before field operations.
