Calculate the height for a specific width and aspect ratio.

calc_aspect_ratio_height.php

<?php
/**
 * Calculate the height for a specific width and aspect ratio.
 *
 * @param int    $width        The width used to generate a height for the aspect ratio.
 * @param string $aspect_ratio The aspect ratio with the ':' as a delimiter. Example: '16:9'.
 * @return string              The calculated aspect ratio height.
 */
function calc_aspect_ratio_height( int $width = 100, string $aspect_ratio = '16:9' ): string {
	// If the aspect ratio is invalid use the default value of 16:9.
	if ( empty( $aspect_ratio ) || false === strpos( $aspect_ratio, ':' ) ) {
		$aspect_ratio = '16:9';
	}
	// Split the string between the delimiter in order to run the aspect ratio calculation.
	list( $divisor, $dividend ) = explode( ':', $aspect_ratio );

	// Cast the divisor and dividend as integers.
	$dividend = intval( $dividend );
	$divisor  = intval( $divisor );

	$quotient = $dividend / $divisor;

	// Check for empty values for quotient assignment and fallback to 16:9 otherwise.
	if ( ( empty( $divisor ) || is_nan( $divisor ) ) || ( empty( $dividend ) || is_nan( $dividend ) ) ) {
		$quotient = 9 / 16;
	}

	// In the case that the quotient is invalid or not a number, use the default aspect ratio.
	if ( is_nan( $quotient ) ) {
		$quotient = 9 / 16;
	}

	$product = $quotient * intval( $width );
	// If this is a float then add at 2 decimal points to number format.
	$decimals = is_float( $product ) ? 2 : 0;

	// Return a regular number format with at least 2 decimal points if the product is a float.
	return number_format( $product, $decimals );
}