Balanza vs. báscula

'Balanza' and 'báscula' are Spanish words that both refer to devices for weighing. However, these two words are not always interchangeable as they refer to different types of scales.

Balanza

A 'balanza' generally refers to a balance scale, which is a type of scale that determines weight by balancing an object with known weights. It often has two plates or bowls suspended at equal distances from a fulcrum.
Mi abuela solía tener una balanza antigua en su cocina para pesar los ingredientes.
(My grandmother used to have an old balance scale in her kitchen to weigh ingredients.)
La balanza del laboratorio se usa para pesar diferentes substancias químicas.
(The laboratory's balance is used to weigh different chemical substances.)
Los comerciantes usan balanzas para pesar frutas y verduras en el mercado.
(Merchants use balance scales to weigh fruits and vegetables at the market.)

Báscula

A 'báscula' tends to refer more towards a platform scale, which could be digital or mechanical, often used for larger or heavier items. They are usually where someone or something is placed on top of it for weighing.
Subí a la báscula para verificar mi peso.
(I stepped on the scale to check my weight.)
El camión pasó por la báscula para confirmar el peso de la carga.
(The truck went onto the weighing scale to confirm the weight of the load.)
En el gimnasio hay una báscula para que los clientes controlen su peso regularmente.
(There is a scale in the gym for customers to regularly monitor their weight.)

Summary

In summary, while both 'balanza' and 'báscula' refer to weighing devices in Spanish, 'balanza' typically refers to a balance scale - often used for smaller objects or ingredients, while 'báscula' denotes a platform scale used frequently for larger or heavier items, including human bodies and vehicles. However, usage can vary by region and context.