update-textarea-rows.pipe.ts

import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
  name: 'updateTextareaRows'
})
export class UpdateTextareaRowsPipe implements PipeTransform {
  transform(fixedRowCount: number,
            expectedCharactersCount: number,
            inputWidth: number,
            fontSize: number
  ): number {
    const averageCharWidth = fontSize / 2; // s. AverageCharWidth of dotNet
    return Math.ceil((expectedCharactersCount * averageCharWidth) / inputWidth);
  }
}