ARRT formula toolkit
The 4 formula toolkits that show up on the ARRT Radiography Boards.
42 formulas organized by clinical domain. Each one carries a worked example, an intuition-first explanation, and practice problems inside the app.
The 4 toolkits
Click any toolkit to see the worked examples (free trial required). Toolkits are sorted by clinical workflow, patient safety first, exposure control next, then image quality, then equipment.
Patient Safety
Quantifying radiation to manage risk and ensure patient safety
- The Language of Dose
- Occupational Dose Limits
- Relative Biologic Effectiveness (RBE)
- Dose Area Product (DAP)
- Controlling Beam Intensity
Exposure Control
Manipulating technique for optimal exposure
- mAs and the Reciprocity Law
- The 15% Rule
- Part Size and Thickness Rules
- X-ray Quantity: mAs and kVp
- Inverse Square Law (Intensity)
- Direct Square Law (Density Maintenance)
- Grid Performance
- Relative Speed Systems (RS)
Image Geometry
Shaping the beam for maximum sharpness
- Geometric Unsharpness (Penumbra)
- Magnification Factor (MF)
Image Capture
Understanding the physics of the final image
- Digital Resolution
- Circuitry and Transformer Physics
- Heat Units and Grid Ratio
- Fluoroscopy and CT
Get the worked examples + practice problems.
The actual formulas, intuition-first explanations, and 50+ practice problems are inside the app. Free tier includes the Patient Safety toolkit complete.
Common questions about ARRT formulas
Do I need to memorize formulas for the ARRT Radiography Boards?
Yes. The ARRT Radiography exam regularly tests calculations including the inverse square law, the 15% rule (kVp/mAs density relationship), density maintenance formula, grid Bucky factor, and unit conversions (rad to gray, rem to sievert). Most are simple algebra once you know which formula applies. Memorization plus 50–80 worked problems is enough to pass this content area.
What are the most-tested ARRT Radiography formulas?
The 15% kVp/mAs rule, the inverse square law (intensity ∝ 1/distance²), the density maintenance formula (mAs₂ = mAs₁ × (D₂² / D₁²)), the Bucky factor (mAs multiplier when adding a grid), Half-Value Layer calculations, equivalent dose (H = D × Wʀ) and effective dose (E = Σ(Wᴛ × Hᴛ)). The toolkit covers 42 formulas across patient safety, exposure control, image geometry, and image capture.
Are these formulas the same as in the Lange Q&A and Mosby books?
Yes. The formulas in our toolkits are the standard ARRT-tested formulas you find in Bushong's Radiologic Science for Technologists, Lange Q&A: Radiography Examination, and Mosby's Comprehensive Review of Radiography. We keep the math identical, the difference is the worked examples and the way each formula is taught with intuition first, then the formula.