The short answer
Work out the total hours the job takes, divide by the hours you have, and add one person if there is any carrying, any deadline, or any chance somebody does not show. Two people who can work in parallel usually beat three who take turns.
Start from hours, not from feel
Estimate how long the job would take one person, in hours. Then divide by the number of hours in your day. That is your crew size before adjustments.
A move that would take one person twenty hours, on a day where you have five usable hours, is a four person job. Guessing two and hoping is how a day turns into a day and a half.
Ask whether the work can actually split
Some work divides cleanly. Carrying, loading, cleanup, and demo all go faster with more hands.
Some does not. One person in a trench, one truck to load, one doorway everything has to fit through. Adding people to a job with a single bottleneck just gives you more people standing near the bottleneck.
The cases where you add one
There are four common reasons to size up rather than down.
- Heavy or awkward items, where a two person carry is the only safe way.
- A hard deadline, like a truck that has to leave or a dumpster that gets picked up.
- A long walk between the work and the vehicle, which eats more time than people expect.
- A crew that has never worked together, which always starts slower than one that has.
The real cost of one too few
Being one person short does not slow a job by a fraction. It usually turns a finished day into an unfinished one, which means paying for a second day, renting the truck again, or losing the slot.
Being one person over costs you one day rate. That is almost always the cheaper mistake, and it is why experienced people round up.
Book them as separate spots
When you post the job, say how many workers you need. It sets expectations, and the people who apply know they are joining a crew rather than working alone.
Give the crew one person to report to. Three workers and nobody in charge is the most reliable way to get a slow morning.
Plan for one not showing
It happens in this work. If the job genuinely cannot run short, hire one more than you need, or line up somebody you can call that morning.
See the guide on handling a no show for what to do at 7 when somebody has not arrived.
This guide is general information, not legal, tax, or insurance advice. Rules differ by state and by situation, so talk to your own professional before you rely on it.