Radiography
Geometric unsharpness (Ug)
Ug from the source size and the exposure geometry, or the shortest source-to-object distance that keeps Ug under a limit.
For reference only — verify against your procedure and the governing code.
Maximum projected source or focal-spot dimension.
From the source side of the object to the film.
Leave blank to use the ASME Section V recommended maximum for the thickness.
Result
- Geometric unsharpness Ug
- 0.228mm
- ASME V T-274.2 recommended max
- 0.02 in. (0.51 mm)
- Minimum d₀ for Ug ≤ 0.51 mm
- 223.5mm
Within the ASME Section V recommended maximum for under 2 in. (under 50 mm).
| Material thickness | Ug maximum |
|---|---|
| under 2 in. (under 50 mm) | 0.51 mm (0.02 in.) |
| 2 through 3 in. (50 through 75 mm) | 0.76 mm (0.03 in.) |
| over 3 through 4 in. (over 75 through 100 mm) | 1.02 mm (0.04 in.) |
| over 4 in. (over 100 mm) | 1.78 mm (0.07 in.) |
Both columns are the code's own values; neither is converted.
Formula
- Ug = F · t / d₀
- d₀ (minimum) = F · t / Ug(max)
Units. Lengths in mm or in.; Ug comes out in the same unit. The ASME recommended maximum is read in the selected system's own numbers — the code prints mm and inch bounds side by side (50 mm against 2 in.), and they are not exact conversions of each other.
Assumptions and limits
- F is the maximum projected source or focal-spot dimension; t is from the source side of the object to the film; d₀ is source to object. t and d₀ in one unit; Ug comes out in F's unit.
- Measure t and d₀ at the approximate centre of the area of interest (ASME V T-274.1).
- The ASME Section V values shown are its RECOMMENDED maximums (T-274.2), by the thickness the IQI is based on. Your referencing code section or procedure may set its own limits.
Sources
- ASTM E94/E94M-17, Standard Guide for Radiographic Examination Using Industrial Radiographic Film — §14.4.2 Eq (1) and its worked example; Table 1 (typical steel HVL).
- ASME Boiler and Pressure Vessel Code, Section V (2025), Article 2 — T-274.1 geometric unsharpness; T-274.2 recommended maximum values.
More radiography calculators
For reference only — verify against your procedure and the governing code.
Standards and documents are cited by their publishers' names to identify them. TRACE is not affiliated with, endorsed by or sponsored by ASTM International, ASME, the U.S. Nuclear Regulatory Commission, NIST or the Laboratoire National Henri Becquerel. Formulas are paraphrased and cited by clause; get the documents themselves from their publishers.