Weight caps how long one hand can hold the device

What it is

A tablet can be held for a while in one hand so the other can open a door, hold a strap, or take a note. Weight caps how long that one-handed hold lasts. A few hundred grams do not announce themselves at the start; after tens of seconds the shoulder and forearm fail first, the device sags, both hands return, or it is set onto any available surface. This is not whether a target is inside a reach envelope—reachable actions can be done before the muscle burns—and it is not the edge covered by a holding hand. This entry is about load bearing, a cap on duration, not the shape of a hot zone.

Why it happens

One-handed support of a tablet is a moment: mass times the lever from the center of mass to the wrist or elbow. A tablet’s area puts that center farther from the support than a phone’s, so the same grams tire more. Portrait lengthens the lever; landscape often forces an awkward grip and an even shorter duration. Fatigue accumulates. For the first seconds people can still tap the upper half; then the hold drops, the reachable set sinks with it, and finally only targets near the supporting hand remain. Protective grip changes—two hands, onto a desk, against a lap—arrive suddenly while the interface is unchanged, and a one-handed action in progress is cut. Cases and keyboard folios add another hundred or two grams; the advertised mass is not the held mass. Standing, walking, the other hand occupied, one-handed support is a real need and the first posture to fail.

Studying it

Use the same shell at different masses (or added weights). Have people hold it one-handed and do light tasks (dismiss a notification, turn a page, reply to a short message). Record time until the first forced switch to two hands or a set-down, and the drop in hold height over time.

Independent variables: device mass, case on or off, posture (sit, stand, walk), portrait versus landscape. Dependent variables: one-handed duration, sag of the hold, fraction of tasks interrupted by fatigue.

Do not measure with the person sitting and the elbow supported—that is a resting forearm, not a hold. Subjective “heavy” and the moment of actually setting it down often disagree; score the behavioral grip change. Phone one-handed durations do not transfer: the lever is different.

Where it stops holding

Use that stays on a desk, a lap stand, or a keyboard dock barely lets weight into the interaction, and one-handed duration is not a constraint. Around seven inches, with mass close to a large phone, one-handed holds last longer, but still tire more than a phone of equal mass because area puts the center farther out. Children and people with shoulder or neck problems have a shorter cap; do not use a young-adult lab mean. When the other hand is gone only briefly (a card swipe, a door), the interface should let one small thing finish in those seconds, rather than assume a one-handed hold can carry a whole session.

Applying it

• Make actions that may happen while the other hand is away short, and place them on the supporting-hand side: a reply, pause, dismiss an alarm. Do not design them as a form that must be finished under a one-handed hold.
• Lay out long tasks for two hands or a desk. Do not write the main path as a sustained one-handed hold.
• Try it at real case weight: stand, hold one-handed, notice when you must switch. Treat that time as the cap on one-handed tasks, not the gram number in the spec.
• Verify standing, one-handed, with a case, walking the steps that must complete while the other hand is away. If they cannot finish, or require a mid-task switch, shorten them further or move the entry to the supporting-hand side.

Related

• Within the group: K3.06.1 How the tablet is held occludes its edges · K3.06.2 A two-handed grip puts the center out of reach
• Adjacent: K3.07 One-handed Reach Degradation on Large Screens · C2.12 Holding Postures · K1.10 One-handed Mode and Large-screen Reach
• Search terms: holding fatigue · tablet weight · one-handed duration