A tape measure quietly stops being a one-person tool somewhere around twenty five feet. Below that there are decent workarounds. Above it, the honest answer is that you need a different tool.
Three things go wrong once you are past arm's reach with nobody at the other end.
The tape sags. A steel tape unsupported across a room bows downward under its own weight, and the path it takes is longer than the straight line you wanted. The reading comes back long, and it gets worse the further you go.
The hook moves. The end hook is deliberately loose by the thickness of the hook itself, so it reads correctly whether you push or pull. Hooked over a baseboard and tugged from across the room, it shifts, rotates, or comes off entirely.
You cannot see both ends. You are reading the number at your end while hoping the far end is still where you left it and still square to the wall. It usually is not.
Under about fifteen feet these are minor. Between fifteen and twenty five they become noticeable. Past twenty five feet a solo tape measurement is a guess with a number attached to it.
If a tape is what you have, these help.
Trap the hook rather than hooking it. Close it in a door, put a heavy object on it, or wedge it into the corner where two walls meet. Anything that stops it rotating.
Run the tape along the floor. The floor supports it, so sag disappears. You then have to account for the baseboard at both ends, but a supported tape with a known correction beats an unsupported one with an unknown error.
Measure in stages. Mark the floor with tape at a known point, measure to the mark, then from the mark onward. Errors add rather than compound, and each individual reading is short enough to be reliable.
Use a rigid rule for short spans. A folding rule or a long spirit level does not sag at all, which makes it more accurate than a tape for anything it will physically span.
This is the job these tools were designed for, and the difference is not simply that it is faster.
With a tape, you are managing two ends of a physical object across a space. With a laser, you stand at one wall, press the back of the tool flat against it, and shoot the opposite wall. There is no far end to manage. Everything you need is in your hand, and the measurement is a straight line by definition rather than by hope.
That changes what is practical alone. Room diagonals become trivial rather than impossible. Ceiling heights need no ladder. A full room takeoff with five readings takes about a minute, and you can do it in an occupied house without moving furniture or asking anyone to hold anything.
Working alone removes the second person who would otherwise catch your mistakes, so a few habits earn their place.
Set the reference point first. Decide whether the tool measures from its front or back edge and set it deliberately. Working alone there is nobody to notice that every reading is out by the length of the tool. This is the most common solo error.
Brace, do not hold. Press the tool flat against the wall rather than holding it out. Freehand introduces an angle you cannot feel, and the reading always comes back long.
Take each reading twice. With nobody checking your work, repeatability is your only verification. If two readings match, move on. If they do not, something is wrong with the setup rather than the tool.
Sketch first, write as you go. Draw the room roughly before measuring anything and write each number onto the sketch immediately. Alone, there is nobody to remind you which wall the 14 ft 2 in belonged to.
Use the minimum in tracking mode. For a diagonal, hold the measure button to enter continuous mode and sweep the far corner. The smallest number is the true perpendicular distance. This is a genuinely useful trick that is difficult to replicate with a tape and a helper.
Being honest about the limits: a laser removes most of the need for a second pair of hands, not all of it.
Anything requiring simultaneous action at two points, like checking a long run for level with a string line, or holding material in position while marking it, still needs help. Very long outdoor runs where you cannot see the dot may need someone holding a target plate at the far end, though a green beam or a unit with a camera viewfinder often solves that too.
For measuring a room, though, the second person is genuinely obsolete. The full room method is here, and if you are buying a tool specifically to work alone, the DIY and homeowner picks are the right starting point.
For the wider picture on choosing a laser measure, including what the specifications actually mean, start on our front page.