ARRT formula toolkit
The 4 formula toolkits for ARRT Radiography Boards prep.
35 formulas, grouped here by clinical domain. Each one carries a worked example and an intuition-first explanation inside the app, which also has 19 practice problems.
The 4 toolkits
The worked examples are inside the app. 5 concept pages are free, with no card. This page groups the formulas into toolkits: patient safety, exposure control, image geometry, then image capture. The app lays the same formulas out as a path of units: Exposure, Geometry, Digital image, Equipment, then Dose and protection.
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
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: image intensifier gain
Get the worked examples + practice problems.
The formulas, intuition-first explanations, and 19 practice problems are inside the app. The free tier includes 5 formula concept pages: inverse square law, mAs and reciprocity, the 15% rule, magnification factor, and grid conversion. The other 13 concept pages come with paid plans, which open soon.
Common questions about ARRT formulas
Do I need to memorize formulas for the ARRT Radiography Boards?
Plan to know them. ARRT publishes topics, such as the inverse square law, not a formula list, and it does not say how many calculations appear. Commonly taught ones include the inverse square law, the 15% rule (kVp and mAs), the density maintenance formula, the grid Bucky factor, and unit conversions (rad to gray, rem to sievert). ARRT says SI units are the primary units of radiation measurement on the exam, so learn gray and sievert first. The ARRT handbook says you cannot bring your own calculator: Pearson gives you a basic four-function calculator if you ask, and basic and scientific calculators are available within the exam.
Which ARRT Radiography formulas are commonly taught?
ARRT does not publish which formulas come up most. Commonly taught ones include 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), and equivalent dose (H = D × Wʀ). The toolkit covers 35 formulas across patient safety, exposure control, image geometry, and image capture.
Where do these formulas come from?
They are the standard forms taught in radiography programs. If your program teaches a different form or value, go by your program. The difference here is the practice problems and the way each formula is taught with intuition first, then the formula.