Free · Unit conversions

Custom Unit Factors, Products & Ratios

Convert quantities using your own nonzero factors, including products, ratios and reverse conversions.

  • 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

If one A equals 100 B, then 2 A equals 200 B. For products, multiply both conversion factors; for a ratio, divide by the denominator factor.

B = A × factor; product factor = factor A→C × factor B→D; ratio factor = factor A→C / factor B→D

Worked example

Enter these known values and leave the other values blank.

B units per one A
100 B
A
2
A units per one B
0.01 A
B
200

Assumptions and limitations

  • Supply factors for compatible dimensions. The calculator applies your factors and cannot establish that independently named A, B, C and D units measure compatible quantities.
  • This is multiplicative conversion. Offset temperature scales, logarithmic units and conversions that need density or another physical property require a different model.
  • Factors must be nonzero. Signed factors and quantities are supported for algebraic scale transformations.

Common questions

Why is the denominator factor inverted?

A quantity per B becomes a quantity per D by dividing by the number of D units in one B. Multiplying the denominator factor would change the rate in the wrong direction.

References

Bookify tests conversion factors for exact nonzero sign, so valid tiny factors are not rejected by approximate numeric equality.

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