Dip-Corrected Interval Calculator
Correct a measured downhole interval to the true thickness of a bed or vein, and optionally to the true vertical depth it represents. A hole cutting a unit obliquely records more length than the unit's real thickness, and an inclined hole gains less vertical depth than its along-hole length. Used by geologists and drillers when logging and reconciling drill data.
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How to use this calculator
- Enter the downhole interval (along-hole length) in metres.
- Enter the angle between the drill-hole axis and the bedding/vein plane (0–90°) for the true thickness.
- Optionally enter the hole inclination from horizontal (0–90°) to also get the vertical interval (depth gained).
How it works
True thickness is the perpendicular thickness of a unit. If a hole crosses the unit at an angle θ to its plane, the along-hole interval overstates the thickness, and true thickness = interval × sin(θ). This is the same sine correction used for true width of tabular bodies.
The vertical correction is separate: a hole inclined at angle i from horizontal gains a vertical depth of interval × sin(i) over that run (a vertical hole, i = 90°, gains its full length; a horizontal hole gains none). Keep the two clear — one converts along-hole length to true thickness across the plane, the other converts along-hole length to vertical depth.
Worked example
8 m interval, 60° to bedding, hole inclined 60°. A hole logs 8 m through a bed, meeting the bedding plane at 60°. True thickness = 8 × sin(60°) = 8 × 0.8660 = 6.93 m. If the hole is also inclined 60° from horizontal, the vertical depth gained over that run = 8 × sin(60°) = 6.93 m.
Common mistakes
- Mixing up the hole-to-plane angle with the hole inclination — they are usually different angles and drive different corrections.
- Measuring the angle from the plane's normal instead of the plane itself; the formula uses the angle to the plane, so a hole perpendicular to bedding meets the plane at 90°.
- Applying the vertical correction to get thickness (or vice versa) — vertical interval is depth, not thickness.
Frequently asked questions
How do I convert a downhole interval to true thickness?
Multiply the interval by the sine of the angle between the hole axis and the plane of the bed or vein: true thickness = interval × sin(angle).
What is the vertical interval correction?
It converts along-hole length to the true vertical depth gained: vertical interval = interval × sin(hole inclination from horizontal). A vertical hole gains its full length; an inclined hole gains less.
Which angle goes where?
The hole-to-plane angle gives true thickness. The hole inclination from horizontal gives vertical depth. Enter the inclination only if you want the depth correction.
When is true thickness equal to the interval?
Only when the hole is perpendicular to the plane (angle = 90°), where sin(90°) = 1.
Is this the same as true width?
The formula is the same sine correction. 'True width' is the term for tabular bodies/veins; 'true thickness' is the term for beds. This tool adds the vertical-depth correction as well.
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