It seems that the constructor does not accept values in the scientific format, e.g. "1e20". To get around this limitation, I wrote a function that converts floats represented by a scientific format string to floats represented by a string as a decimal fractional number. You can use the output of this function as the input to the constructor.<?phpuse BCMath\Number;$num = -123e-40; $strNum = sci2dec( $num ); $L = new Number( $strNum );var_dump( $L );function sci2dec( string $s ): string{ if( !preg_match( '/^([+-]?)(\d+(?:\.\d+)?)[eE]([+-]?\d+)$/', $s, $m ) ) return $s; [ $sign, $mantissa, $exp ] = [ $m[1], $m[2], (int)$m[3] ]; [ $int, $frac ] = str_contains( $mantissa, '.' ) ? explode( '.', $mantissa, 2 ) : [ $mantissa, '' ]; $digits = $int . $frac; $exp -= strLen( $frac ); if( $exp >= 0 ) { $digits .= str_repeat('0', $exp); $dec = lTrim($digits, '0'); return $sign . ( $dec === '' ? '0' : $dec ); } $pos = strLen( $digits ) + $exp; if( $pos > 0 ) return $sign . subStr( $digits, 0, $pos ) . '.' . subStr( $digits, $pos ); return $sign . '0.' . str_repeat( '0', -$pos ) . $digits;}?>Output is:object(BcMath\Number)#2 (2) { ["value"]=> string(43) "-0.0000000000000000000000000000000000000123" ["scale"]=> int(40)}