BED Calculator

Created by Łucja Zaborowska, MD, PhD candidate
Last updated: Nov 30, 2021

The BED calculator is a simple way to assess the biological effect of radiotherapy treatment. You can find both the biologically effective dose and the equivalent total dose in 2-Gy fraction (EQD2).

In the article below we will explain BED calculation formula, the BED dose usage, and the theoretical basis of our radiotherapy dose calculator.

💊 Check the dosage calculator if you're looking for a typical drug dose calculation.

How to use the BED calculator?

In order to use our BED calculator, you'll need the following data:

  1. The duration of the irradiation, either:

    • Less than few minutes; or

    • Longer than few minutes - a slowly delivered fraction is a way to lessen the side effects of the treatment. In this case, we'll need one extra variable, dose rate factor, which describes the repairability of a cell (takes values of <1).

  2. α/β ratio - describes tissue radiation sensitivity. The higher the α/β, the more sensitive the tissue:

    • Late reacting tissue has an α/β of 3;

    • Early reacting tissue has an α/β of 10; and

    • The central nervous system or kidneys have an α/β of 2.

  3. Dose given per fraction - dose received during single irradiation (in Grays - Gy).

  4. Total dose given - the sum of all the doses received. It is equal to the number of fractions multiplied by the dose in one fraction (in Grays - Gy).

  5. Your results will be given in Grays (Gy) - the unit of ionizing radiation in the .

While you're at it, try the following topics:

Use of BED calculation in radiotherapy

The biologically effective dose (BED) formula, created in 1989, is an efficient way of defining the treatment expectations. It helps clinicians make decisions regarding further treatment and its quantitative assessment. The BED equation is based on the linear dependence of cells' survival, used in radiobiology.

BED is mostly used to compare different types of treatment and report research results. If the researcher wants to be more precise, they should include a few different BED equations using different α/β ratios for different tissues involved in a neoplasmic process and/or the tissues surrounding them. You may also add different BED results to receive the final dose of the treatment.

Biologically effective dose is constantly mistaken for biological equivalent dose in radiation therapy.

BED formula in radiation

The commonly used formula, and the one found in our BED calculator, looks as follows:

BED = Total dose * (1 + (Fraction dose / αβ))

The biologically effective dose formula changes when the irradiation lasts for more than a few minutes:

BED = Total dose * (1 + [(g * Fraction dose )/ αβ ])


  • g = Dose rate factor of intracellular repair; and
  • αβ = α/β ratio.

How you ever wondered how much radiation you usually absorb during a flight? ✈️

The EQD2 calculator

We've also decided to add the EQD₂ function to the BED calculator - to save you time! If you still want to compute it by yourself, here's the equation you'll need:

EQD₂ = Total dose * ((Fraction dose + αβ) / (2 + αβ))


  • αβ = α/β ratio.

EQD₂ is an equivalent of a total dose served in 2 Gy fractions.

Łucja Zaborowska, MD, PhD candidate
Irradiation duration
< few minutes
α/β ratio
Dose per fraction
Total dose
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