The throw ratio determines how far your projector needs to be from the screen to achieve a particular image width. This value is set by the built-in lens – similar to a camera, where the lens determines how much of the scene fits into the frame from which distance. That is why not every projector can be used anywhere you like: the mounting location defines the optics required. Whether ceiling, shelf or low sideboard – the throw ratio is just as decisive when buying as brightness and resolution. The following sections explain which throw ratio suits which room situation. If you are in a hurry: on every product page in the shop – for example the BenQ W4100i or another model from the category Home cinema projectors – the image size calculator instantly gives you the right image width for your desired distance, with no formula and no theory.
At a glance
- Formula: throw distance = image width × throw ratio – and vice versa.
- Three classes: standard throw/long throw (TR > 1.0), short throw (TR 0.4–1.0), ultra short throw/UST (TR < 0.4). The limits are industry convention, not standardised.
- The zoom range gives positioning flexibility: fixed lens = one distance, 1.2× zoom = little leeway, 2× zoom = comfortable reserve.
- “Throw ratio” and “projection ratio” refer to the same dimensionless figure.
- If you are looking for ready-made room combinations rather than theory: see our guide Projector to screen distance.
- What is the throw ratio?
- Throw ratio – one figure, several names
- The three throw ratio classes: standard, short throw, ultra short throw
- Zoom range and positioning flexibility
- Calculating throw ratio: three formulas
- Short throw and ultra short throw: when special optics are worthwhile
- From data sheet to room: calculator and practice
- Frequently asked questions (FAQ)
What is the throw ratio?
The throw ratio describes the relationship between the projector’s distance from the screen and the width of the projected image. (The distance is measured from the lens, not from the back of the housing – a detail that is often overlooked when planning a room. More on this in the calculator section.) It is a dimensionless number that is stated in data sheets either as a single value (fixed lens) or as a range (zoom lens, e.g. 1.35:1 – 2.73:1). Wide-angle optics are below 1:1, classic home cinema lenses in the range 1.2:1 to 2.0:1, and telephoto lenses for large halls reach values of 7:1 or more.
The clever part: if you know a projector’s throw ratio, you can derive the required distance from any image width – and vice versa. This makes the throw ratio the most important figure in the data sheet, right after brightness and resolution. In every purchase, it decides whether the projector you want will physically fit into the room at all.
A projector consists of three components in the light path: light source, internal display panel and lens. The throw ratio is a property of the lens. Installation projectors with interchangeable lenses cover throw ratios from about 0.3:1 to 8:1 with different lenses, making the same projector body usable for wall projection in a foyer and long-throw projection in a lecture hall.
Throw ratio – one figure, several names
“Throw ratio” is the internationally common term found in data sheets; some manufacturers also call it the “projection ratio” – both refer to the same figure. Two related terms often crop up when you are researching:
- Throw distance or projection distance – the absolute distance in metres (not the ratio).
- Lens-to-screen distance – another synonym for throw distance.
So when a manufacturer writes “throw ratio 1.5:1”, it means: one unit of image width needs 1.5 units of distance. With an image width of 2 m, this gives a throw distance of 3 m. The unit does not matter – the value works identically in metres, centimetres or inches.
The three throw ratio classes: standard, short throw, ultra short throw
The throw ratio itself is unambiguous – the figure is in the data sheet. The only point of contention is the value from which a projector counts as “short throw” or “ultra short throw”: these thresholds are industry convention but not standardised by DIN or ISO, and individual manufacturers draw the line slightly differently. For values close to a limit (e.g. TR 0.42 or 1.03), we check the data sheet carefully in our advice rather than relying on the marketing label. The following division into three classes is the map we use to bring order to these fluid transitions – it determines which room geometry suits the device:
| Class | Throw ratio | Typical distance (at 2 m image width) | Main advantage |
|---|---|---|---|
| Standard throw / long throw | > 1.0 | 2.4–4.0 m | Widest choice of models, widest zoom ranges |
| Short throw | 0.4–1.0 | 0.8–2.0 m | No shadows cast, good for small rooms |
| Ultra short throw (UST) | < 0.4 | 0.1–0.4 m | Close to the wall, TV replacement, no ceiling mounting |
Standard throw / long throw (LT) – TR > 1.0
The classic case: projector under the ceiling or on a shelf behind the seating position. Typical values are between 1.2:1 and 2.0:1 – this covers 90 % of all home cinema and conference room installations. From around TR 2.5:1, the choice of models on the market becomes considerably thinner; home cinema flagships such as the Epson EH-QB1000W reach into this range with their zoom range. For long-throw ranges from 3:1 (lecture halls, churches, large event venues), the route usually leads to installation projectors with interchangeable lenses – such as the Panasonic PT-MZ882WEJ, which can be fitted with a short, standard or long-throw lens depending on the application. In this class, the overall setup becomes correspondingly more demanding in terms of price. “Long throw” and “standard throw” are used synonymously on the market; some manufacturers reserve “long throw” specifically for these telephoto ranges.
Short throw (ST) – TR 0.4–1.0
Shorter distances, fewer shadows, less space required. Short-throw projectors are preferred in classrooms, meeting rooms and small home cinemas where a classic long-throw setup is not possible for structural reasons. The BenQ TK700ST (the “ST” in the product name stands for short throw), for example, produces a 100″ diagonal image (approx. 2.21 m wide) from a distance of about 2 m – ideal for gaming setups in the living room. The Optoma UHZ35ST covers the same application with a laser light source and 4K.
A typical case from our advisory work: a customer with a wall distance of 3.80 m in the living room wanted a 120″ image diagonal (approx. 2.66 m wide). A standard home cinema projector with a throw ratio of 1.50:1 would have needed a distance of 4.00 m – 20 cm too far. Bottlenecks like this are not only caused by the wall depth itself: there is often a crossbeam, a ceiling spotlight or a lamp on the ceiling exactly where the projector would actually need to go. And there must also be clearance at the back – depending on the cable, HDMI or power plugs protrude 5 to 10 cm from the housing, which further reduces the usable space. Instead of investing in a premium model with a larger zoom, the TK700ST was the more economical choice: short throw with a throw ratio of 0.9:1 delivers the 120″ image from 2.40 m, and the remaining metre of room depth was left for the seating position and cable routing. The right throw ratio was more important here than the higher product class.
For school use or presentation environments, it is worth taking a look at our category Short-throw projectors – where you will find the complete selection.
Ultra short throw (UST) – TR < 0.4
Projectors with a throw ratio below 0.4 project from right next to the wall – typically 20 to 40 cm from the screen for a 100″ diagonal (approx. 2.21 m wide). In the home cinema segment, this makes them a genuine alternative to a TV: no trip wire, no projector above the sofa and, with laser TVs with an integrated smart system, no separate media player either. The Hisense PX3-Pro with a throw ratio of 0.22:1 and 3,000 lumens is a typical example – Xbox-certified, 4K HDR, triple laser engine. For bright living spaces with more ambient light, the Epson EH-QS100W with 4K UHD and a laser engine provides additional brightness reserves.
In a business environment, UST projectors play to their strengths in two scenarios. Conference rooms with limited room depth or glass-wall architecture, where a classic ceiling or table setup is structurally difficult: a model such as the BenQ LU960UST+ with 5,200 ANSI lumens and WUXGA resolution produces the presentation image from just a few centimetres from the wall – the presenter does not walk into the picture, and the whiteboard next to it remains usable. Digital signage in retail, foyers and reception areas is the second field: the device disappears almost invisibly on the wall, customers do not walk into the beam path and, with a laser light source such as the DuraCore engine in the Optoma ZH430UST, the system is designed for long daily operating times.
By design, UST devices usually have no optical zoom. The wall distance alone determines the image size – this makes exact positioning critical, but it is a simple relationship. A CLR screen (ceiling light rejecting) is essential with UST projectors, because standard fabrics reflect ambient light at a shallow angle and wash out the image.
Zoom range and positioning flexibility
The zoom range indicates how flexibly image width and distance can be varied in relation to each other – without moving the projector.
- Fixed lens (one value, e.g. 1.20:1): Exactly one distance per image width. Precise positioning required, low price, typical of entry-level DLP, many UST models and current lifestyle projectors such as the JMGO N1S Ultimate.
- 1.1× zoom (e.g. 1.50–1.65:1): Narrow leeway, enough to compensate for tolerances when ceiling-mounting, but not for free choice of position. Typical of budget-conscious home cinema entry models such as the Acer H6815BD with 4K UHD and 4,000 lumens.
- 1.5× to 2× zoom (e.g. 1.40–2.24:1): Comfortable reserve. You can position the projector within a generous corridor and fine-tune the image size using the zoom – standard on premium home cinema models, such as the Optoma UHZ58LV with 1.6× zoom, dual laser light source and 4K UHD.
- Interchangeable lens (installation segment): Maximum range. A lens with a throw ratio of 0.38:1 makes the same projector body UST-capable, while a 4.0:1 telephoto lens serves large halls.
One limitation is important: lens shift and throw ratio are independent of each other. The standard position for ceiling mounting is projector upside down, lens roughly level with the top edge of the screen – this corresponds to the native offset of most models and works without lens shift. If you need more flexibility in positioning, you will find the right options in the lens shift guide.
Calculating throw ratio: three formulas
Three simple rearrangements cover every calculation. In everyday planning and advice, these three are all you need:
(1) Distance from image width: throw distance = image width × throw ratio
Example: projector with a throw ratio of 1.50:1, desired image width 2.5 m → 2.5 × 1.50 = 3.75 m distance.
(2) Image width from distance: image width = throw distance ÷ throw ratio
Example: fixed ceiling position 4 m from the wall, projector with a throw ratio of 1.50:1 → 4 ÷ 1.50 = 2.67 m image width.
(3) Working out the throw ratio: throw ratio = throw distance ÷ image width
Rarely needed for planning, but helpful if you want to measure an existing installation: projector is 3 m from a 1.5 m wide projection → TR = 3 ÷ 1.5 = 2.0:1.
A little conversion help: diagonal in inches → image width (16:9)
Data sheets and marketing texts often give the diagonal in inches, while the formula above works with the image width in metres. Multiply the diagonal in inches by 0.0221 to get the image width in metres (the factor applies to the standard 16:9 aspect ratio).
- 100″ diagonal → 2.21 m width
- 120″ diagonal → 2.66 m width
- 150″ diagonal → 3.32 m width
For 16:10 (business projectors with WUXGA), the factor is 0.0215; for 21:9 (Cinemascope home cinema), 0.0234.
Zoom lenses are given two values in the data sheet (e.g. 1.35:1 – 2.73:1). This range gives two valid distances for each image width – between these two limits the projector can be positioned freely, and the image size is adjusted with the zoom. Entry-level models with a narrower zoom (e.g. 1.20:1 – 1.30:1) offer less positioning leeway; models with 2× zoom offer a comfortable reserve in practice.
Short throw and ultra short throw: when special optics are worthwhile
The question “short throw or standard?” is often the first fork in the road in our advice. Some situations clearly favour shorter throw ratios:
- Positioning close to the wall / no space for ceiling mounting: A rented flat without permission to drill, a living room without space for a classic long-throw setup, an office with a low ceiling – UST or short throw solve the problem.
- No shadow from the presenter: In classrooms and meeting rooms, the presenter naturally stands in front of the screen. With standard throw they cast themselves into the picture; with short throw or UST they do not.
- Laser TV as a TV replacement: If you want to replace a classic 65″ or 75″ TV with a 100″ or 120″ image, there is hardly any way around UST. Laser TVs combine a UST projector with integrated Android/Google TV, soundbar and streaming apps – installation straight out of the box, no media player needed.
Standard throw nevertheless remains the most productive class: the widest choice of models, the widest zoom ranges, the most flexible optics. If you have the choice and enough room depth, this is where you get the best value for money and the most freedom in positioning. You will find a detailed selection including specific application scenarios among our short-throw projectors in the shop.
From data sheet to room: calculator and practice
For concrete room planning, we provide an image size calculator on every product page in the shop. You enter either the planned distance or the desired image width, and the calculator gives you image width, image height and diagonal – for models with a zoom lens, for both ends of the range. This is particularly helpful if you are torn between several models and want to check which one actually suits your room geometry.
If you want to measure the room before comparing specific models (distance between screen, seating position and projector location), it is worth taking a look at our practical guide Projector to screen distance. There you will find guideline values for seating distance, screen size and the most common room situations. This article explains the theory behind the figure – the distance guide provides the ready-made combinations for everyday use.
An experience from our advisory work: many customers start with the question “How far away does the projector need to be?” – and only realise later that the same question the other way round is much more interesting. “How big will my image be with the 3.50 m I have?” is the more honest basis for planning and spares you the bitter realisation shortly before installation that the projector you want needs an extra half metre the room cannot give. The throw ratio provides both answers – depending on how you rearrange the formula.
An important planning fact: the throw ratio refers to the distance from the lens. Do not measure from the back of the housing. On classic standard and short-throw models, the lens sits practically at the front edge of the housing – so the formula applies directly to the distance between the screen and the front of the device. For the actual mounting position, also allow for the housing depth (typically 30–50 cm, more for installation projectors) and cable clearance at the back. The calculated value is therefore the distance from lens to screen, not the length the projector takes up in your room.
On ultra short throw and laser TV models, the lens is not at the front edge by design but set back within the housing. The pure throw ratio value only gives a rough guide here – what counts is the manufacturer’s distance table from the manual, which lists the specific wall-to-screen distance for each image width. For most models in our range, you will find this table directly in the product description in the shop.
For proper planning, the following also applies: if in doubt, the official manufacturer documentation counts, not forums or third-party sources. Distinguish between the data sheet and the manual. The data sheet provides key technical values (throw ratio range, offset, zoom, lens shift limits). The detailed distance table for each image size, on the other hand, can be found in the projector’s manual. The major manufacturers provide both documents as PDFs on the product page; a good example is the official Epson documentation for the EH-QS100 with clearly presented distance information. Real-world building conditions (wall plaster, furniture tolerances, uneven screed) cost a few centimetres per metre in practice – that is no drama, but it should be taken into account when choosing the zoom range. A 2× zoom comfortably absorbs this, a fixed lens does not.
Frequently asked questions (FAQ)
What does throw ratio mean for a projector?
The throw ratio describes the ratio of throw distance to image width – a dimensionless figure determined by the built-in lens. A projector with a throw ratio of 1.5:1 produces an image 1 m wide from a distance of 1.5 m. You will often find the term “throw ratio” in data sheets; some manufacturers also call it the projection ratio – both mean the same value.
How do I calculate the projector distance from the throw ratio?
Multiply the desired image width by the throw ratio. Example: 2.5 m image width × TR 1.50 = 3.75 m throw distance. For the other direction (image width from a fixed distance): image width = distance ÷ throw ratio. An image size calculator is also available on every product page in the shop.
From what value is a projector a short-throw or UST model?
Standard throw begins above TR 1.0. Short throw lies in the range 0.4 to 1.0. Ultra short throw (UST) reaches values below 0.4 – typically 0.18 to 0.25 for current laser TVs and UST models such as the Hisense PX3-Pro (TR 0.22:1) or the Epson EH-QS100W.
What does a throw ratio with two values mean, e.g. 1.35–2.73:1?
Two values indicate a zoom lens. The projector can be positioned freely within this range, and the image width is adjusted with the zoom. The wider the range, the more flexible the positioning. A 1.5× to 2× zoom (e.g. 1.35–2.73) offers a comfortable positioning reserve in a home cinema, while a 1.2× zoom is only enough for fine adjustment.
Does lens shift affect the throw ratio?
No. Lens shift and throw ratio are independent of each other. The zoom determines image size and distance; the shift only moves the finished image parallel to the lens axis – without changing distance or image width. If you want flexible positioning, you need both: the right zoom range for the room depth and lens shift for vertical positioning. Details in the lens shift guide.
The perfect home cinema or a properly designed conference room needs more than just the right throw ratio. Our projector specialists will advise you personally on the optimal setup – from choosing the right lens and the right screen to the cables. Or browse our projector category, short-throw projectors or ultra short throw projectors directly – with the formula you have just learned, you can sort any data sheet in no time.
Matching product categories in the shop:
Further guides:
- Lens shift on projectors – detailed guide with model examples
- Projector to screen distance – table and formula for the distance
- Projector A–Z – glossary of projection technology & projector terms – glossary of technical terms
