Why depth is really about viewing distance
A desk's depth decides one thing above all: how far back your screen can sit. The front of the desk is taken up by the keyboard and your forearms, and whatever is left behind that is the room the monitor has to move into. So the question "how deep should the desk be" is mostly the question "how far from my eyes do I want the screen", and the two answers have to agree. The Health and Safety Executive puts the screen "about an arm's length away" from you, and our guide on how high your monitor should be works through what that distance feels like and how to hit it. The depth of the desk is simply what makes that distance possible or not: too shallow and the screen is pushed towards you with nowhere to retreat; deep enough and it sits back where the HSE line puts it, with the keyboard still in front of it on the same surface.
The common UK sizes, and why they are a starting point
Walk through UK desk listings and two depth figures come up again and again. Around 600mm is the shallow, space-saver end, the depth of a narrow desk built to tuck into a box room or against a landing wall. Somewhere between 700 and 800mm is what the furniture sellers tend to call comfortable for a full setup, with a monitor behind a keyboard and a little desk left over. Treat both as common sizes rather than a rule, because the sellers themselves disagree on where the line falls, and the depth that is right for you depends on your own reach and your screen, not on a number that happens to repeat. What the range is good for is reading a listing: a desk quoted at 500mm is going to put the screen close whatever you do, and one at 800mm gives you the room to set the distance yourself.
How to measure the depth you actually need
You can work out your own figure in a minute with a tape measure, and it beats any number off a listing. Sit at your desk the way you really sit, reach one arm out to where the screen will go, and mark where your fingertips land: that reach, give or take, is where the front of the screen wants to be. Now add the part of the screen that sits behind that point. A monitor on its own foot needs the depth of the stand as well, which on many stands runs a hand's breadth or more from the front of the panel to the back of the base. Add the keyboard room in front, a palm's depth so your wrists are not jammed against the desk edge, and you have the depth the desk has to provide. Measure it, then hold it against the depth the listing quotes in the maker's own figure. If your number comes out larger than the desk, the screen will sit closer than arm's length, and that is the point to either find a deeper desk or change how the screen is mounted.
When a monitor arm changes the sum
The one thing that rewrites all of this is how the screen is held. A monitor on its bundled stand spends desk depth twice over: once for the base plate and again for the gap the base needs behind the panel. Take the stand away and that depth comes back. A monitor arm clamps to the back edge of the desk and holds the screen out over the surface, so the panel can sit near the back edge, or even slightly beyond it, and still be pushed to arm's length on a desk a stand would never allow. That is why a shallow desk and an arm are such a common pairing in a small room: the arm buys back the depth the desk does not have. It does not make depth irrelevant, since you still need room for the keyboard and somewhere for the clamp to grip, but it is the difference between a 600mm desk that feels cramped and one that works. If the real question is whether a desk will fit the room at all, that is a footprint decision, and our guide to the best standing desk for a small home office takes the width and the floor space from there.
FAQ
Q: Is there a standard home office desk depth in the UK? A: Not a single one. The figures that recur on UK listings sit between roughly 600mm for a space-saver and 700 to 800mm for a fuller setup, but retailers quote them differently and none of it is an agreed standard. What settles your own depth is your reach and the screen you use, so treat those numbers as a sanity check on a listing rather than a target to hit.
Q: Is a 600mm deep desk enough for a monitor? A: It can be, and it often has to be in a small room, but it is tight once a monitor sits on its own stand, because the stand eats into the depth you have left for viewing distance. The two ways to make 600mm work are a monitor with a shallow stand, or a monitor arm that holds the screen off the desk so the base no longer takes up room. If neither is an option and the screen ends up close to you, a deeper desk is the simpler fix.
Q: Does desk depth matter more with two monitors? A: It matters in the same way but across a wider arc. Two screens side by side each want to sit about an arm's length away, which on a shallow desk is hard to manage for both at once, especially if they are angled in towards you. A deeper desk gives them room to sit back, and an arm or a twin arm that holds them off the surface does the same job on a desk that cannot spare the depth. Set the screen you use most to the right distance first, then bring the second one to match.