Direct Proportion Calculator

Work out direct proportion instantly with clear inputs, formula shown and shareable results.

About Direct Proportion Calculator

In direct proportion y = kx, so the ratio y/x is constant. Finding k from the known pair lets you compute y for any other x.

Formula

Direct proportion

y = kx, so y₂ = y₁ · x₂ / x₁

Worked example

With the default values below, Direct Proportion Calculator returns Corresponding y of 17.50000000. Change any input above and every figure here is recalculated in your browser.

Inputs used

First x: 4
First y: 10
Second x: 7

Results

Corresponding y: 17.50000000
Constant of proportionality k: 2.50000000
y₂ / x₂ (should equal k): 2.50000000
Change in x: 75.0000 %

Step by step

1Values used
2Direct proportion
3Corresponding y= 17.50000000
4Constant of proportionality k= 2.50000000
5y₂ / x₂ (should equal k)= 2.50000000
6Change in x= 75.0000 %

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 8 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

If 4 items cost 10, what do 7 cost?

k = 2.5 per item, so 7 items cost 17.5.

How do I spot direct proportion?

The graph is a straight line through the origin, and doubling x doubles y.