DPI is dots per inch, which in a digital context, means pixels per inch.
So ….
1 inch at 300 dpi is 300 pixels.
2 inches is 600 pixels.
It sounds as if you’ve been asked to create something 1.51×300 pixels tall, by 1.01×300 pixels tall. So I’d wager it would be 453 pixels tall by 303 pixels wide.
Steve