Free · Measurement and planning

Proportional Image Resize Dimensions

Resize a rectangle proportionally from original dimensions and one new dimension, and show its linear size percentage.

  • Formula & worked example
  • Private in your browser
  • No signup
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

For the worked example, secondImageHeight = 300.0000000, percentage = 50.00000000.

New height = new width × original height / original width.

Worked example

Enter these known values and leave the other values blank.

Image ratio
Custom
First image height (H1)
600
First image width (W1)
800
Second image width (W2)
400
Second image height (H2)
300
Percentage change (A)
50 %

Assumptions and limitations

  • Width and height must use the same measurement unit.
  • Percentage is new linear size as a percent of original size; it is not area percentage or percentage increase. Custom dimensions avoid ambiguous preset orientation.
  • Results follow the stated ideal arithmetic model. Display rounding does not change the underlying calculation.
  • Supply sufficient known values and leave the desired quantity blank. Controls retain captured inverse branches and units.
  • If a retained lock prevents a reverse calculation, unlock the quantity you want to solve before supplying the known values.

Common questions

What does the worked example demonstrate?

New height = new width × original height / original width.

Can I change the measurement units?

Available selectors convert the entered physical quantity. Use compatible units for all related quantities.

Why can a result be blank?

A missing input, invalid denominator or underdetermined relationship cannot provide a unique finite result.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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