Rule of three (proportion)

Client

Classic direct proportion—if 2 items cost 5, how much for 8 items?

About Rule of three (proportion)

Solve a:b = c:x for x—direct proportion helper. The interactive transform on this page runs in your browser tab—Toolcore does not need your paste for the core operation described above.

How to use this page

Paste or type in the main workspace, run the primary action from the toolbar, then copy or download the result. Use Load example when the page offers it, or URL prefill (?q= / ?qb=) so agents and tickets open the same input.

x ≈ 20.000000 (because 2:5 = 8:x)

Nearby workflows on Toolcore

  • Ratio simplifier — Reduce ratio a:b to lowest terms using GCD—whole-number ratios in your browser. when units or numeric output should be checked on a related calculator.
  • Percent change — Calculate percentage increase or decrease from an old value to a new one—local math in your browser. when units or numeric output should be checked on a related calculator.
  • Weighted average calculator — Mean of values with weights—one value per line as “value weight”—computed locally. when units or numeric output should be checked on a related calculator.
  • Unit converter (length, temperature, weight) — Length (metric & US customary), temperature (°C, °F, K), and weight (mg to lb)—paste one value, see every column. when units or numeric output should be checked on a related calculator.

Common use cases

  • Rule of three (proportion) for quick local checks without uploading data.
  • Copy results into tickets, docs, or classroom notes.

Common mistakes to avoid

  • Unexpected input shape

    See the intro and how-to notes for accepted formats.

FAQ

Is processing local?

Yes—this runs entirely in your browser.

Agent prefill?

Open the page directly—multi-field inputs are not URL-prefilled.

More tools

Related utilities you can open in another tab—mostly client-side.