Calculadora Regla de 3

Introduce tres valores conocidos y obtén el cuarto valor automáticamente. Selecciona el tipo de proporción y la precisión deseada.

Valores de Entrada

Cálculo en tiempo real activo
Magnitud 1
A
B
=
Magnitud 2
C
X

Resultado de la Proporción

X = 60
10/20 = 30/X -> X = 60 (Direta)

Fórmula y Solución

X = (B x C) / A
X = (20 x 30) / 10
X = 600 / 10
X = 60
Ratio A/B
0.50
Ratio C/X
0.50
Factor
x2.00
Type
Direta
Cómo Funciona

Cómo funciona la Calculadora Regla de 3

Resuelve cualquier problema de proporción en 3 pasos sencillos sin memorizar fórmulas.

La Calculadora Regla de 3 es una herramienta online gratuita que resuelve proporciones de forma automática e instantánea.

1
?

Introduce 3 Valores

Escribe los 3 valores conocidos en A, B y C. El valor X se calculará automáticamente.

2
A B C X

Multiplicación Cruzada

La calculadora aplica la multiplicación cruzada A × X = B × C (directa) o A × B = C × X (inversa).

3
X

Resultado Instantáneo

El resultado de X aparece al instante junto a la fórmula detallada paso a paso.

Ejemplo Práctico

Si 5 obreros hacen un trabajo en 12 días, ¿cuántos días tardarán 8 obreros?

Type: Inversa (más obreros → menos días)
Formula: X = (A × B) ÷ C = (5 × 12) ÷ 8
Result: X = 7,5 días

Real-Time Calculation

Updates instantly as you type without clicking any button.

Step-by-Step Formula

Shows complete formulas, ratios, and scaling factors for easy learning.

Direct & Inverse

Switch between direct proportion (grows together) and inverse proportion (grows oppositely).

Custom Precision

Adjust decimal precision from 0 to 6 places or full precision.

Formula

Rule of Three Formulas

Master direct and inverse Rule of Three formulas step by step.

Direct

Simple Direct Rule of Three

When quantities change in the same direction

A B
=
C X
Result
X =
B × C A
1 Set proportion: A is to B as C is to X
2 Cross multiply: A × X = B × C
3 Solve X: divide both sides by A
Inverse

Inverse Rule of Three

When quantities change in opposite directions

A B
=
X C
Result
X =
A × B C
1 Identify inverse relationship between quantities
2 Invert second ratio: A/B = X/C
3 Solve X: X = (A × B) ÷ C

Proportion

Equality between two ratios is called a proportion

Cross Multiplication

Multiply means and extremes to solve equations

Quantities

Check whether relation is direct or inverse before solving

Calculators

Specialized Calculators

Choose the perfect calculator optimized for your specific math problem.

Simple Rule of Three

Direct proportion between two quantities

Inverse Rule of Three

When one quantity increases as the other decreases

Simple & Compound

Compare both rule of three calculators side-by-side

Compound Rule of Three

Proportions involving multiple quantities

Percentage Calculator

Calculate percentages using Rule of Three

Nursing Math

Dosage, drip rate, and microdrip calculations
FAQ

Preguntas Frecuentes

The Rule of Three is a mathematical method to find an unknown fourth value from three known values using proportion.

In direct rule of three, when one quantity increases, the other increases. In inverse rule of three, when one increases, the other decreases proportionally.

Set up the proportion, determine if it is direct or inverse, and apply cross multiplication to solve for X.

If both quantities grow or shrink together, it is direct. If one grows while the other shrinks, it is inverse.