Compare Projected Text Size With a Viewing-Distance Threshold You Set — Free
A slide’s font setting does not reveal the capital-letter height on the screen. Estimate visual angle from measured letter height and audience distance, then compare it with a threshold chosen for your event.
The proof surface
Caption-reading audits estimate text speed over time. This sightline estimates angular size of projected capital letters at a seat; it does not evaluate typeface legibility or certify a room.
Why the flat version breaks
Using font points instead of projected millimetres
The display system scales a slide; measure the output on screen.
Measuring from the projector lens
Distance is from viewer to screen, not projector to screen.
Treating an angle as a legibility pass
Typeface, contrast, vision, glare and personal needs are not captured by the formula.
How to work the projection angle sightline
Use the actual projected letter height in millimetres, not the font size in a slide editor. Projection scale can change the physical result.
Use metres from the screen plane to the seat or viewing position. Check the farthest positions you want to include.
Arcminutes ≈ 3438 × letter height in millimetres ÷ (distance in metres × 1000). The output is geometric and uses small-angle approximation.
The example threshold is invented, not a visual-acuity standard. Check contrast, glare, movement, room lighting and participant feedback in the actual space.
What the projection angle sightline replaces
| Question | Before | Visible working |
|---|---|---|
| Using font points instead of projected millimetres | The display system scales a slide; measure the output on screen. | Measure distance from screen |
| Measuring from the projector lens | Distance is from viewer to screen, not projector to screen. | Compute the approximate angle |
| Treating an angle as a legibility pass | Typeface, contrast, vision, glare and personal needs are not captured by the formula. | Set a threshold with the audience in mind |
A local arithmetic aid replaces hand calculation, not expert review. No paid AI service is needed.
Run it on the samples, right here
FIRST-LOAD
Input is processed locally and a draft is saved automatically in this browser profile when storage is available. Reset to sample clears that draft; Pro history has its own clear button. A state link encodes your inputs in its URL: share only non-sensitive rows. Browser history, clipboard and anyone receiving the link may retain it. Optional AI use below leaves this device; it is not required.
Geometry only, not optometry, visual-accessibility or building-code advice. This is not a compliance test. Ask audience members what they can read, provide alternatives and have a qualified accessibility professional assess critical presentations.
Data note: Everything runs in this browser tab on the projection angle sightline: your slide | capital-letter height mm | viewing distance metres stays on this device, nothing is uploaded, and the reading is rebuilt only when you press run.
Go deeper: the companion app files the same reading as a climbing rung ladder
The article demo above runs without limits. The companion app keeps a local history, exports the rows as CSV, prints the projection angle sightline reading, and holds your drafts on this device — one free run, then $ 4 one-time for the layer that keeps filing.
The projection angle sightline reading is complete for free. The optional $4 layer adds print, row CSV and the last five local reading summaries; it does not add hidden answers. Checkout is not configured yet; the article demo remains unlimited.
Open the compare projected text size with a viewing-distance threshold you set companionBoundary
Geometry only, not optometry, visual-accessibility or building-code advice. This is not a compliance test. Ask audience members what they can read, provide alternatives and have a qualified accessibility professional assess critical presentations.
What this is built on
- Method: the equation is stated next to the result and uses only quantities entered by the reader.
- All sample records are invented examples. No standard, tariff, product rate, schedule or policy is fetched or represented as verified.
- For any threshold or rule, use the current value from the provider, handbook or qualified professional responsible for it.
Before: The display system scales a slide; measure the output on screen. After: the projection angle sightline shows the working beside each named row so the reader can change the assumption and inspect the consequence.
Optional AI formatting, not calculation
For this projection angle sightline, an external AI text tool may help format non-sensitive notes if you already use one. No AI service or account is required: manual entry completes the same free core calculation. Do not paste private or sensitive data. Review every value against the source before using it.
Format my non-sensitive notes for a projection angle sightline. Return plain rows only: slide | capital-letter height mm | viewing distance metres. Preserve supplied quantities exactly. Do not guess missing values; list questions separately. Do not calculate or add advice. I will check every row before pasting into the local tool.
Accepted schema: slide | capital-letter height mm | viewing distance metres. No AI response is executed as code.
Walk three labelled examples
First reading. The invented sample Back row | 6 | 8 uses minimum visual angle in arcminutes = 3. The displayed smallest measured visual angle is 2.57850 arcminutes. Follow the row note back to the measurements and conversion rather than treating the headline number as a recommendation. The sample is deliberately concrete so the reader can reproduce the arithmetic by hand.
Changed assumption. The alternate input Large title | 10 | 8 produces 4.29750 arcminutes for the displayed summary. Compare it with the first reading to see which entered quantity moves the result. In a real plan, change only the assumption that has a traceable source; do not tune a value just to make a row pass.
Boundary case. With Near threshold | 7 | 8 and the same setting, the worked result is 3.00825 arcminutes. This case shows how the arithmetic behaves at a useful edge, not that the underlying process has been measured or verified. Check the boundary statement beside the result and confirm any consequential input with the responsible person before acting.