True Width from Intercept Length Calculator
Convert a downhole intercept length into the true (perpendicular) width of a tabular body such as a vein, lode or mineralised zone. Because a drill hole rarely cuts a structure at right angles, the logged core length overstates the real width — this tool applies the standard sine correction. Used by exploration geologists, resource geologists and core loggers.
Enter Values
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How to use this calculator
- Enter the downhole intercept (core) length in metres, measured along the hole.
- Enter the acute angle α between the drill-hole axis and the plane of the structure (0–90°).
- Read the true perpendicular width and the true/intercept ratio; use 'Try an example' to see a worked case.
How it works
A drill hole that pierces a tabular body at an angle records a longer core length than the body's actual thickness. If α is the acute angle between the hole axis and the plane of the body, the true (perpendicular) width equals the intercept length multiplied by sin(α).
When the hole is perpendicular to the plane (α = 90°) the intercept equals the true width and the ratio is 1. As the hole becomes more oblique the ratio sin(α) shrinks, so the true width is always less than or equal to the logged intercept. Knowing the full hole orientation (plunge/azimuth) and structure orientation (dip/dip-direction) lets you compute α from first principles; here you enter that acute angle directly.
Worked example
12 m intercept at α = 55°. A hole logs a 12 m intercept through a sulphide vein. The acute angle between the hole and the vein plane is 55°. True width = 12 × sin(55°) = 12 × 0.8192 = 9.83 m. The ratio is 0.819, so the logged core overstates the true width by about 22%.
Common mistakes
- Using the obtuse angle instead of the acute angle between the hole and the plane — always take the angle ≤ 90°.
- Confusing the intercept-to-plane angle with the dip of the structure; they are only the same when the hole is vertical.
- Reporting the raw core length as 'width' in a resource estimate without applying the sine correction.
Frequently asked questions
What is the difference between intercept length and true width?
Intercept length is the distance measured along the drill core through the body; true width is the perpendicular thickness of the body. True width = intercept × sin(angle between hole and plane), so it is always ≤ the intercept.
What angle do I enter?
The acute angle (0–90°) between the drill-hole axis and the plane of the tabular body. If the hole is perpendicular to the plane, enter 90°; if it grazes almost parallel to the plane, enter a small angle.
Why is my true width smaller than the core length?
Because sin(α) ≤ 1 for any angle up to 90°. The only time true width equals intercept length is when the hole meets the plane at exactly 90°.
Do I need the hole plunge and azimuth?
Not for this tool — it uses the acute angle directly. For a full 3D solution from hole plunge/azimuth and structure dip/dip-direction, compute the angle between the hole vector and the plane's pole, then use that as α.
Is this the same as the dip-corrected interval?
The maths is identical (length × sine of the angle to the plane). This tool is framed for tabular-body width; the dip-corrected interval tool is framed for bedding/vein thickness and adds a vertical-depth correction.
Related tools
- Dip-Corrected Interval Calculator
- Dip & Dip Direction to Trend & Plunge Converter
- Core Recovery Calculator
- RQD Calculator
- Composite Assay by Length Calculator
- Downhole Depth Interval Calculator
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