SFFPC.io · Small-form-factor planning bench
Fit it on paper first.
A datasheet-style bench for builders who care about size, thermals and fit. Work out case volume, test GPU, cooler and power supply clearances, size a PSU with honest headroom, and follow a build order that does not cable you into a corner.
- Case envelope—
- External volume—
- Suggested PSU—
- Build progress—
Sheet index
Four instruments- 01Case volumeMillimetres or inches in, litres out, with an isometric model that resizes as you type.Open
- 02Clearance checkerGPU length, cooler height and PSU form factor against the case, with pass, tight or fail and the margin in millimetres.Open
- 03Power budgetYour component watts plus headroom, rounded to a suggested PSU rating.Open
- 04Build orderA checklist of 26 steps in the sequence that keeps every connector reachable.Open
Why small builds are unforgiving
Fit is a hard limit
In a full tower, a long card is a preference. In a small case it is pass or fail: if the card is longer than the bay, nothing else on the spec sheet matters. Millimetres count, and so does the space you need for power connectors and the cables behind them.
Heat has nowhere to go
Less volume means less air to absorb heat and shorter paths between hot parts. Cooler height, fan placement and cable routing change temperatures far more here than in a roomy chassis, and the litre figure is the first number worth knowing about any case.
Power is sized by the smallest supply that fits
Compact power supplies come in fewer shapes, so the form factor your case accepts narrows your options before you choose a wattage. Knowing your real draw, with headroom you can defend, tells you whether a given form factor can do the job at all.
Order of assembly is part of the design
The part you install first often decides whether the part you install last still fits. A build order is a plan for reaching every connector while you still can, and it is much cheaper to write down than to discover with a screwdriver.
Reading the spec rail
The dark panel on the left (or behind the Spec rail button on a phone) follows you from sheet to sheet. It is a live readout of everything you have entered: the case envelope and volume, your clearance margins, the power budget and how far along the build checklist you are.
Change a number on any sheet and the rail updates immediately. The small isometric model at the top of the rail is the same case drawn to the same scale, so you can see a dimension change without leaving the page.
Your inputs are kept in this browser so the rail agrees with itself from page to page. If your browser blocks storage, the numbers still work within a page but will not carry across pages. Press Reset bench at any time to return to the illustrative starting values.
Those starting values are examples, not recommendations. Replace every one of them with a figure from your own parts' data sheets before you rely on a result.
PSU envelopes
mmFig. 2. Side elevation, drawn to one scale. The dashed outline shows how much of the SFX-L envelope an SFX unit leaves empty.
| Form factor | L | W | H |
|---|---|---|---|
| SFX | 125 | 63.5 | 100 |
| SFX-L | 125 | 63.5 | 130 |
| ATX | 150 | 86 | 140 |
Assumptions and limits
This bench has no parts catalogue and makes no claims about any product. Case limits, card lengths, cooler heights and wattages are all things you type in, taken from the manufacturer's own specification for the exact item you intend to buy. The tools do the arithmetic, show the margins and flag what is tight. They cannot know what your sources got wrong.
Clearance checks compare single dimensions. They do not model cable bend radius, radiator thickness, memory height, card thickness or airflow, and a pass here is a reason to keep planning rather than a guarantee. The power budget works from sustained watts and a headroom percentage you choose; it is a sizing aid, not a safety certification.
SFFPC.io is an independent project and is not affiliated with any case, component or power supply maker. If you spot a wrong constant or an edge case the tools mishandle, write to hello@sffpc.io.