Spring Weights and Swaps: Matching Force Curves to Your Hands

Switch listings quote force in grams-force, usually as a single number. That number is ambiguous unless the vendor says which point on the travel it refers to. Actuation force is the force required at the point the switch registers, roughly two millimetres down on a standard MX switch. Bottom-out force is the force required to reach the end of travel at four millimetres. The two can differ by twenty grams or more on the same switch, so comparing one vendor's actuation figure with another's bottom-out figure is meaningless.

Spring behaviour follows Hooke's law: force is proportional to compression, with the constant of proportionality being the spring rate. This is why a switch's force curve is a straight line for linears, and why you can predict the force at any depth if you know two points. Our spring swap calculator does exactly this arithmetic, converting between actuation and bottom-out figures for any spring length so you can compare products honestly.

A standard MX spring is about 14 mm uncompressed. Long springs run 18 to 22 mm and extra-long springs go beyond that. Because a longer spring is already partly compressed when installed, it starts with more preload — the force present before you touch the key. The practical result is a curve that begins heavier but rises more slowly, so the gap between actuation and bottom-out narrows. Typists describe this as a more consistent, less mushy press.

Slow springs are a variant wound from thinner wire with more coils, giving a very low rate and a soft, gradual build. Progressive springs use variable coil spacing so the rate increases as you press, producing a light top and a firm floor that discourages heavy bottom-out. Two-stage springs do the same in a coarser, more abrupt way. None of these is exotic to install; they all drop into the same housings and cost a few units per hundred.

Most people converge on 55 to 67 grams bottom-out for daily typing. Below about 45 grams, accidental actuations become common for anyone who rests fingers on the home row. Above about 75 grams, finger extensor fatigue sets in within a couple of hours for most hands. Gaming preferences skew lighter for rapid repeated presses; heavy-handed typists who slam keys often prefer heavier springs because the extra resistance slows the impact.

The cheap way to find your number is a spring sampler: buy a pack containing five or six weights, swap them into a single switch, and type a paragraph with each. Do the test on your actual board, since plate stiffness and keycap mass change the perceived weight noticeably. Write down your reaction immediately — after the third spring your memory of the first is unreliable. Two hours of this saves a great deal of money compared with buying full switch sets speculatively.

Swapping springs means opening every switch, which is the same operation as lubing and best done at the same time. You need a switch opener matched to your housing brand, a tray to keep parts organised, and patience. Work in batches of ten: open, lift out the stem, replace the spring, reassemble, snap shut. Check that the spring seats squarely on the bottom housing post; a spring sitting at an angle produces a scratchy, uneven press and is the most common mistake.

Springs sometimes ping — a metallic ring caused by the coils vibrating freely inside the housing. A very light application of thin oil on the spring, or a quick bag-lube where you shake springs in a bag with a few drops of lubricant, kills nearly all of it. Do not over-apply: excess oil migrates onto the stem legs and can dull a tactile bump. Around one drop per fifty springs is plenty.

Once you have done one full swap, consider varying weight by position. The little fingers are the weakest and control shift, control, tab, caps and enter — often the keys held longest. Fitting springs ten to fifteen grams lighter on those positions while keeping the index and middle finger keys at your normal weight noticeably reduces end-of-day fatigue. Heavier springs on the spacebar are also common, since the thumb is strong and the wide key benefits from extra return force.

Track the change objectively. Use the ergonomics calculator to check your desk and wrist geometry at the same time, because spring weight is only one of the variables that determines whether typing hurts. If your wrists are extended fifteen degrees upward because the board is too tall, no spring weight will fix that. Solve posture first, then tune force, and treat the two as one system rather than as unrelated hobbies.

Keep a small reference set once you have settled. Three or four switches built with your candidate springs, kept in a tester, cost almost nothing and let you re-audition weights years later when your hands, desk or workload change. Preferences genuinely shift: people who type all day frequently drift lighter over time, while people who game competitively often drift heavier to reduce accidental presses under pressure. Having physical references means that drift is something you can measure rather than guess at, and it saves you from repeating the entire sampler exercise every time a new switch release tempts you into thinking the problem is the housing rather than the spring inside it.