How do you perfectly cook a 1" top sirloin on a Gas Grill to medium rare every time?

I don’t know about all the hood up and down and blah blah blah, but here’s how you can tell how done your steak is…

First, find the big mushy muscle at the base of your thumb. (The abductor pollicis brevis and flexor pollicis brevis).

Touch your thumb to your pinkie and press on that muscle. That’s well done.
Ring finger = medium well
Middle finger = medium
Index finger = medium rare
Touching no fingers = rare

Thanks, never heard that before.
But I was looking for answer like sear both sides one minute each, than close for 3 minutes, flip 2 minutes after the grill has reached 400 degrees. A person I knew had a system that was good and consistent.

Pray to the Grill Gods.
Pray good and hard.

From chef husband: It depends on how dense the muscle structure is, the fat ratio in it. There’s no exact time, each time. Things to consider: is it semi cold outside or 90 degrees outside? There are too many factors to do it just one way every single time.
Take it, sprinkle salt and pepper, olive oil..put it on the grill and cook it til it’s done. People tend to over-complicate steaks, let the meat speak for itself.

^ That was my husband’s words. I know nothing about cooking.

Season it with salt and pepper and let it sit for a few minutes. Get the grill good and hot, hood up, grill for 4–5 minutes on one side. Flip it, turn the heat down, and stick a constant-read meat thermometer into it, and grill it until it reaches 130–135 degrees. Take it off the grill and let it sit for 5 minutes. Perfect medium rare.

If you’ve got experience, you can tell the doneness by the firmness of the meat, as @essieness suggests, but that’s not something I’d recommend for a beginner. Also, if you have experience with lots of steaks and that particular grill, you can probably estimate how long it will take without needing a meat thermometer. But the meat thermometer is the only way to be sure.

(You can also do this indoors—season the steak, get a cast iron pan good and hot, and cook the steak for 5 minutes on that side. You will get smoke. If you don’t get smoke, you’re doing it wrong. Then flip it and put the whole pan into a 400–450 degree oven, with the meat thermometer as above, until it reaches 130–135. Put the steak on a plate and let it sit for 5 minutes before serving.

Let steak sit out for 30 minutes. Sear with lid open over direct high heat for 4 minutes. Turn steak over and finish cooking for 7 minutes with lid closed.

Lots of good answers. I like the 4 minute/7minute flop as a guide, and the thumb muscle comparison.

Another good tip is to make sure you let it sit out and get to room temperature before you start cooking. Then just use the meat thermometer like suggested above. Good luck.

I hate using a meat thermometer on a thin piece of meat…juices run out and can make the meat a little dry.

Mine has a tiny little tip. I also poke carefully, and can usually stop any juise loss very quickly.