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Window Width & Level Calculator

Calculate the Min and Max HU range from Window Width & Center.

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Inputs

HU
HU

Your values stay on this device.

Results

Visible HU Range
Black Point (< Min)-160
White Point (> Max)240

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Assumptions

  • The math assumes a simple centered window calculation and does not model viewer-specific rendering nuances.
  • Display appearance still depends on monitor calibration, reconstruction, and the actual image data.
  • Window settings help visualization, but they do not replace careful review of the original acquisition and full imaging context.

Sensitivity preview

Window Width (WW) -10%: Visible HU Range -140 to 220 HU

Window Width (WW) Current: Visible HU Range -160 to 240 HU

Window Width (WW) +10%: Visible HU Range -180.00000000000003 to 260 HU

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About this Window / Level

In CT imaging, the human eye cannot distinguish all 4096 shades of gray typically captured by the scanner. 'Windowing' restricts the display to a specific range of Hounsfield Units (HU) relevant to the tissue being examined. Values below the range appear black; values above appear white.

Who this calculator is for

  • Radiology trainees, technologists, and anyone learning how CT display presets work.
  • People who already have a window width and level from a viewer or protocol.
  • Learners connecting tissue-specific presets with the underlying HU range.

When to use it

  • Use this calculator when translating a named CT window into explicit black and white cutoffs.
  • Use it to compare how different width and level choices emphasize soft tissue, lung, or bone.
  • Use it in teaching when explaining why the same CT dataset looks different under different presets.

How to use this calculator

  1. Enter Window Width (WW) (the range of contrast).
  2. Enter Window Level (WL) (the center point).
  3. The result shows the Min (Black) and Max (White) HU values.

Key assumptions

  • The math assumes a simple centered window calculation and does not model viewer-specific rendering nuances.
  • Display appearance still depends on monitor calibration, reconstruction, and the actual image data.
  • Window settings help visualization, but they do not replace careful review of the original acquisition and full imaging context.

Accuracy and testing

Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.

View accuracy page

How this calculator works

Min HU = Level - (Width / 2) Max HU = Level + (Width / 2) Any pixel with HU < Min is black. Any pixel with HU > Max is white. Pixels in between are shades of gray.

Inputs explained

Window Width

Controls contrast. A narrow width (e.g., 80 HU for brain) increases contrast. A wide width (e.g., 1500 HU for lung) displays a broader range of densities.

Window Level

Controls brightness. It sets the midpoint of the gray scale. It should be set close to the average density of the tissue you are viewing.

Example scenarios

Soft Tissue

WW 400, WL 40. Range: -160 to 240 HU.

Lung

WW 1500, WL -600. Range: -1350 to 150 HU.

Bone

WW 1800, WL 400. Range: -500 to 1300 HU.

Key Features

  • Instant Calculation
  • Private & Secure
  • Mobile Optimized

Tips & Best Practices

  • Use 'Lung Windows' to see vessels in the air-filled lungs.
  • Use 'Bone Windows' to see detailed fractures in bright bone structures.

Glossary of Terms

Hounsfield Unit (HU)
A quantitative scale for describing radiodensity. Water = 0 HU, Air = -1000 HU.
ROI
Region of Interest. A tool used to measure the average HU in a specific area.

Frequently Asked Questions

What is Window Width (WW)?
Width determines contrast. A narrow width (e.g., 80) creates high contrast (black vs white). A wide width (e.g., 1500) shows many shades of gray.
What is Window Level (WL)?
Level determines brightness. It sets the midpoint of the gray scale. It should be set close to the HU of the tissue you want to examine.
Formula?
Min HU = Level - (Width / 2). Max HU = Level + (Width / 2).