Gray (Gy) — SI Absorbed Dose
The gray is the SI unit of absorbed radiation dose: 1 joule of energy deposited per kilogram of matter. 1 Gy = 100 rad. Used in radiation therapy and food irradiation.
Radiation Converter
Convert between gray/s, sievert/s, rad/s, rem/s, roentgen and all radiation dose rate units — including roentgen to gy, gray to rem, sv to gy, gy to sievert, and more.
⚠️ Important: Radiation measurements require careful handling. This tool provides technical conversions only. Always consult qualified professionals for safety decisions.
Enter a number (e.g., 100 or 1.23e-4)
Enter a numeric value to convert. Scientific notation supported (e.g., 1.23e-4).
Result updates automatically
Copied!
Radiation Unit Conversion Guide
Whether you need to do a quick roentgen to gy calculation, convert gray to rem for legacy dosimetry, or perform any conversion of radiation units for medical physics or safety work, the cards below give you exact formulas and context.
Roentgen to Gy
The roentgen (R) is a legacy unit of radiation exposure. Converting roentgen to gy requires an intermediate step via tissue-absorbed dose: in soft tissue, 1 R ≈ 0.00877 Gy (0.877 rad).
1 R ≈ 0.00877 Gy
Gray to Rem
When converting gray to rem, multiply by 100 (assuming a radiation quality factor of 1, valid for X-rays, gamma rays, and beta particles). This is the standard gray to rem conversion used in legacy US regulations.
1 Gy = 100 rem
Sv to Gy (Sievert to Gray)
For standard radiation types (quality factor = 1), sv to gy conversion is 1:1. For neutrons or alpha particles, divide the sievert value by the appropriate weighting factor before expressing as gray.
1 Sv = 1 Gy (QF = 1)
Gy to Sievert
The gy to sievert conversion accounts for the biological effectiveness of different radiation types. For X-rays, gamma, and beta radiation: 1 Gy = 1 Sv. For alpha particles: 1 Gy = 20 Sv.
H (Sv) = D (Gy) × WR
Gy to Rem
Gy to rem is one of the most common radiation unit conversions in medical physics. Since 1 Gy = 100 rad and 1 rad = 1 rem (for QF = 1), the result is straightforward: multiply by 100.
1 Gy = 100 rem
Rem to Gray
Rem to gray is the reverse of the gy-to-rem conversion. Divide your rem value by 100 to get gray. This is frequently needed when converting radiation units from older US dosimetry records into SI units.
1 rem = 0.01 Gy
Radiation Measurement Conversion
Radiation measurement conversion spans four quantity types: absorbed dose (Gy/rad), equivalent dose (Sv/rem), exposure (C/kg / roentgen), and activity (Bq/Ci). Use the converter above for any conversion of radiation units across all categories.
Converting Radiation Units
Converting radiation units correctly matters for patient safety and regulatory compliance. The calculator on this page functions as a full radiation converter calculator, covering dose-rate, absorbed dose, equivalent dose, and activity units.
Radiation Conversion Formulas — Quick Reference
All formulas assume a radiation quality factor (WR) of 1 unless stated otherwise.
| Conversion | Formula | Example | Use Case |
|---|---|---|---|
| Roentgen → Gy | Gy = R × 0.00877 | 100 R = 0.877 Gy | Legacy exposure to absorbed dose |
| Gray → Rem | rem = Gy × 100 | 1 Gy = 100 rem | SI to US legacy dosimetry |
| Sv → Gy | Gy = Sv ÷ WR | 5 Sv = 5 Gy (QF=1) | Effective to absorbed dose |
| Gy → Sievert | Sv = Gy × WR | 2 Gy = 2 Sv (QF=1) | Absorbed to effective dose |
| Gy → Rem | rem = Gy × 100 | 0.5 Gy = 50 rem | Medical physics, NRC reporting |
| Rem → Gray | Gy = rem ÷ 100 | 200 rem = 2 Gy | Legacy records to SI |
| Rad → Gray | Gy = rad × 0.01 | 500 rad = 5 Gy | Radiotherapy archives |
| Sv → Rem | rem = Sv × 100 | 1 Sv = 100 rem | International to US standards |
Radiation Units Explained
Sievert (Sv) — SI Effective Dose
The sievert accounts for biological impact of different radiation types. 1 Sv = 100 rem. The gy to sievert relationship depends on the radiation weighting factor WR.
Rad — Legacy Absorbed Dose
Non-SI unit of absorbed dose. 1 rad = 0.01 Gy. Still encountered in older medical literature and legacy equipment. When converting radiation units from older records, rad → gray is a common first step.
Rem — Legacy Effective Dose
Non-SI effective dose unit. 1 rem = 0.01 Sv. Rem to gray (via rem → rad → Gy) is frequently needed when reconciling historical US dosimetry data with modern SI records.
Roentgen (R) — Exposure Unit
Measures ionization in air. Converting roentgen to gy requires a tissue conversion factor. In air: 1 R = 8.77 mGy; in soft tissue: 1 R ≈ 9.57 mGy.
Watt/Kilogram (W/kg)
Equivalent to gray per second (Gy/s). 1 W/kg = 1 Gy/s. Used for specific absorption rate (SAR) in electromagnetic field measurements.
Radiation Safety Context
- Natural background radiation: ~2–3 mSv/year
- Chest X-ray: ~0.1 mSv
- CT scan (chest): ~7 mSv
- Occupational annual limit: 20–50 mSv/year
- Public annual limit: 1 mSv/year (excl. natural background)
Common Radiation Conversions
| Unit | Equivalent To | Common Usage |
|---|---|---|
| 1 Sievert (Sv) | 100 rem | Effective dose (biological impact) |
| 1 Gray (Gy) | 100 rad | Absorbed dose (physical energy) |
| 1 rem | 0.01 Sv | Legacy dosimetry |
| 1 rad | 0.01 Gy | Medical radiation therapy |
| 1 W/kg | 1 Gy/s | SAR measurements |
| 1 R (roentgen) | ≈ 0.00877 Gy | Historical exposure records |
Frequently Asked Questions — Radiation Unit Conversion
How do I convert roentgen to gy?
To convert roentgen to gy, multiply the roentgen value by 0.00877. For example, 100 R × 0.00877 = 0.877 Gy. The roentgen measures ionization in air, so the exact roentgen to gy factor varies slightly by tissue type (typically 0.00877 Gy/R in air, ~0.00957 Gy/R in soft tissue).
What is the gray to rem conversion formula?
The gray to rem conversion is: rem = Gy × 100. This applies for radiation with a quality factor (QF) of 1, such as X-rays, gamma rays, and most beta particles. For high-LET radiation like alpha particles (QF = 20), the gray to rem factor becomes ×2000.
How do I convert sv to gy (sievert to gray)?
For the sv to gy conversion, divide the sievert value by the radiation weighting factor WR. For X-rays and gamma radiation (WR = 1): 1 Sv = 1 Gy. For fast neutrons (WR = 10–20): 1 Sv = 0.05–0.1 Gy. Use the calculator above for instant sv to gy results.
How does gy to sievert conversion work?
Gy to sievert conversion uses the formula: Sv = Gy × WR. The radiation weighting factor accounts for biological effectiveness. For gamma/X-ray/beta: WR = 1 (so 1 Gy = 1 Sv). For alpha particles: WR = 20 (so 1 Gy = 20 Sv). This gy to sievert relationship is fundamental to radiation protection dosimetry.
What is the gy to rem conversion?
The gy to rem conversion is: rem = Gy × 100 (for QF = 1). This is because 1 Gy = 100 rad, and for most radiation types 1 rad = 1 rem. The gy to rem conversion is widely used in US medical physics and NRC regulatory reporting.
How do I convert rem to gray?
Rem to gray conversion: Gy = rem ÷ 100. For example, 500 rem ÷ 100 = 5 Gy. The rem to gray conversion is essential when updating historical US dosimetry records (measured in rem) to modern SI units (gray).
What is radiation measurement conversion, and why does it matter?
Radiation measurement conversion is the process of expressing a radiation quantity in different units while preserving the physical meaning. Accurate conversion of radiation units is critical in medical physics (treatment planning), health physics (dose limits), nuclear engineering (reactor safety), and environmental monitoring. Errors in converting radiation units can have serious safety consequences.
Is this radiation converter calculator suitable for professional use?
This radiation converter calculator provides accurate unit conversions for educational and professional reference. For clinical treatment planning, regulatory submissions, or safety-critical decisions, always verify results with qualified health physicists and follow applicable regulatory guidelines.