3D rendering glossary
Render speed: what it is and key factors
Rendering speed is the time it takes a computer to calculate an image or a frame from a 3D scene. It is measured as time per image in photorealistic rendering and in frames per second (fps) in real time. It depends on the hardware, the engine, the complexity of the scene and the quality required.
How rendering speed is measured
There are two worlds with different metrics:
- Offline or production rendering: measured as time per image. A photorealistic architectural image in 4K can take from a few minutes to several hours, depending on the scene.
- Real-time rendering: measured in fps. A video game or an interactive walkthrough needs at least around 30 fps to feel smooth, and virtual reality usually requires 72 to 90 fps or more.
In animation, the total time multiplies: a one-minute video at 30 fps is 1,800 frames, and each extra second per frame adds half an hour to the total calculation.
In practice: Render Fabrik is a 3D architectural rendering studio working with clients in Brazil and Europe, with a quote within 24 hours.
Factors that affect rendering speed
| Factor | Why it matters |
|---|---|
| Resolution | Time grows with the number of pixels: a 4K image has four times more pixels than Full HD |
| Sampling (samples) | More samples per pixel reduce noise but lengthen the calculation |
| Global illumination and bounces | Each additional light bounce multiplies the calculations |
| Complex materials | Glass, reflections, refraction, translucent materials (SSS) and hair are expensive |
| Geometry | Dense vegetation, grass and highly detailed furniture add millions of polygons |
| Number of lights | Many small lights, especially in night interiors, generate noise that is hard to clean |
| Effects | Depth of field, motion blur, volumetric fog and caustics |
| Hardware | CPU cores, GPU power and memory, available RAM |
CPU, GPU and render farms
CPU rendering
Engines such as Corona or V-Ray CPU use all processor cores. They are very stable with huge scenes because they use system RAM, which is usually abundant.
GPU rendering
V-Ray GPU, Redshift, Octane, Cycles, Lumion, D5 Render or Unreal Engine use the graphics card. They tend to be much faster in scenes that fit in GPU memory. The limit is VRAM: if the scene doesn't fit, the render fails or slows down.
Render farms
A render farm distributes the work across many computers. It is the usual solution for long animations: each machine calculates different frames in parallel. There are in-house studio farms and cloud services paid per use.
How to speed up a render without losing quality
- Use denoiser: AI denoisers (such as NVIDIA OptiX or Intel Open Image Denoise) let you stop the render earlier and clean up the remaining noise.
- Optimise geometry: use proxies and instances for vegetation and repeated elements, and remove what the camera doesn't see.
- Adjust textures: don't use 8K maps on objects that occupy few pixels in the image.
- Preview in low resolution: approve framing, light and materials with quick renders and leave the high resolution for the end.
- Limit bounces and samples: set only what's necessary for the scene.
- Render by regions: recalculate only the part of the image that changed after a revision.
Rendering speed in architecture, property development and product design
In architecture, speed determines how many material and lighting tests fit into a project. In property development, it affects the delivery time of off-plan sales campaigns, especially when they include video. In product design, a good setup lets you efficiently generate dozens of colour variants of the same model. In all cases, advance planning saves more time than hardware: a design change after the final render forces the calculation to be repeated.
Speed in a visualisation studio
A visualisation studio balances quality and calculation time on every commission. Interior 3D images, with lots of glass and artificial light, require a different strategy from exterior views, and 3D video requires optimising every frame. If you're looking for a team for your project in Spain, visit our Spain page.
Frequently asked questions
How long does it take to render a 3D image?
It depends on the scene, resolution and hardware. A simple view can take minutes and a complex interior in high resolution can take hours. Real-time rendering generates images almost instantly, with slightly less precision.
Which is faster, rendering with CPU or GPU?
In general, GPU is faster if the scene fits in its memory. CPU is more stable with very large scenes and some complex effects.
Why does my render have noise?
Because not enough samples were calculated. It is solved by increasing samples, improving lighting or using a denoiser.
How many fps does a real-time walkthrough need?
To look smooth on screen, at least around 30 fps and ideally 60. In virtual reality, higher rates are recommended to avoid motion sickness.