Welcome back to Estimation and Sense of Scale! This is lesson four out of five, so we are almost at the finish line. Over the first three lessons, we built mental benchmarks for lengths, weights, and volumes. Each time, the core strategy was the same: anchor to something familiar, then scale up or down. In this lesson, we turn to two quantities that shape nearly every plan we make: time and speed.

How long will dinner take to cook? Can we walk to the café in fifteen minutes? Is a 60-mile highway commute really doable in 30 minutes? Estimating durations and speeds is something we do every day, often without realizing it. Our goal here is to make those mental estimates more dependable by giving them the same benchmark-and-compare structure that has worked so well for length, weight, and volume.

Unlike a length we can hold a ruler against or a weight we can heft in our hands, time has no physical shape. We cannot look at an activity and "see" how long it takes the way we might eyeball the height of a shelf. That can make time feel harder to pin down.

The good news is that most routine activities fall into surprisingly stable ranges. A shower does not last two seconds one day and three hours the next. Familiar tasks repeat often enough that our internal clock is already roughly calibrated. What we need is a short list of duration benchmarks to sharpen that clock, just as we used a coffee mug to anchor volume estimates in the previous lesson.

Below is a table of common activities and their typical durations. These are everyday averages, not world records or extreme cases.

A helpful way to remember these is to sort them into rough time buckets: tasks that take a few minutes, tasks that take about half an hour, and tasks that take about an hour or more. When estimating a new activity, first ask which bucket it belongs to, and then refine from there.

As you may recall from earlier lessons, anchoring to familiar references is the key to good estimates. For travel speed, we can anchor to five everyday ways of getting around. The table below gives values in both mph and km/h.

Two anchors are especially worth memorizing. Walking at 3 mph is the single most useful speed benchmark because nearly everyone walks, and the pace barely changes from person to person. Highway driving at about 60 mph is handy because it simplifies mental math beautifully: at 60 mph, every mile takes exactly one minute.