Telescope Aperture Comparison (Meters)
How big is the ELT mirror? Compare 11 telescope apertures, from ELT 39 m to Hale 5.1 m. ESO and observatory specs with converter. All 11 apertures ranked.
Visual comparison
All values
Click any row to load it as Entry A.
| Name | Value | Context | Source |
|---|---|---|---|
| Extremely Large Telescope 39 m. Top row here. 798 segments. | 39 m (128 ft) | ESO Chile, first light 2029 | ESO ELT FAQ and facts: 39 m mirror; ESO construction proposal: ELT 39 m; Wikipedia ELT table: 39.5 m |
| Thirty Meter Telescope 30 m. Northern ELT hope. | 30 m (98.4 ft) | Maunakea preferred, 492 segments | ESO construction proposal: TMT 30 m; arXiv ELT era article: TMT 30 m; Wikipedia ELT table: 30.0 m |
| Giant Magellan Telescope 24.5 m. 25.4 light surface. | 24.5 m (80.4 ft) | Las Campanas Chile, seven mirrors | ESO construction proposal: GMT about 24 m; arXiv ELT era article: GMT 25.4 m surface; Wikipedia ELT table: 24.5 m |
| Gran Telescopio Canarias 10.4 m. Largest working eye. | 10.4 m (34.1 ft) | La Palma Spain, single mirror | Observatory specs: GTC 10.4 m single segmented primary, La Palma |
| Keck I and II 10 m each. Twin tens. | 10 m (32.8 ft) | Maunakea Hawaii, twin domes | Observatory specs: W. M. Keck twin 10 m segmented primaries; ESO FAQ: current largest up to ten metres |
| Subaru Telescope 8.2 m. Japanese flagship. | 8.2 m (26.9 ft) | Maunakea Hawaii, single mirror | Observatory specs: Subaru Telescope 8.2 m primary |
| Very Large Telescope unit 8.2 m each. Four UTs. | 8.2 m (26.9 ft) | Paranal Chile, four units | Observatory specs: ESO VLT 8.2 m unit telescopes; ESO ELT FAQ: VLT class context |
| Gemini North and South 8.1 m each. Twin pair. | 8.1 m (26.6 ft) | Hawaii and Chile, twin sites | Observatory specs: Gemini twin 8.1 m primaries |
| Magellan Baade and Clay 6.5 m each. Twin pair. | 6.5 m (21.3 ft) | Las Campanas Chile, twin scopes | Observatory specs: Magellan twin 6.5 m primaries |
| MMT Observatory 6.5 m. Matches Magellan. | 6.5 m (21.3 ft) | Arizona, single enclosure | Observatory specs: MMT 6.5 m primary |
| Hale Telescope 5.1 m. Lowest row here. | 5.1 m (16.7 ft) | Palomar California, 1948 glass | Observatory specs: Palomar Hale 5.1 m (200 inch) primary |
About this converter
Optical apertures run 5.1 to 39 m in this table. ELT leads at 39, TMT follows at 30 and GMT at 24.5. GTC sits at 10.4, Keck twins at 10 each, Subaru and VLT units at 8.2 each and Gemini twins at 8.1 each. Magellan and MMT twins sit at 6.5 each with Hale closing at 5.1. One ELT mirror matches almost eight Hales. ELT, TMT and GMT stay unfinished with first light years noted. Every figure here is the observatory primary diameter.
How to use it
Pick two telescopes and a unit in the top row. The three boxes below stay linked. Change any box and the other two update. Try 1 ELT against Hale mirrors to see the 39 versus 5.1 gap in meters or feet.
Values pin single mirror equivalent diameters with multi mirror counts noted. GMT 25.4 light surface rows as 24.5 equivalent, which the table notes. Radio dishes stay out because optical only is the topic. Interferometer baselines stay out because they measure arrays, not mirrors. First light years ride in context where set. Collecting areas ride in sources with ELT near 1000 square meters. Adaptive optics generations stay noted where they sharpen a row.
FAQ
What is the biggest telescope?
ELT at 39 m in Chile, first light 2029. It gathers 15 times the light of 10 m scopes.
What are the other giant telescopes?
TMT at 30 m and GMT at 24.5 m. Both stay unfinished with sites and years noted.
What is the biggest working telescope?
GTC at 10.4 m in La Palma. Keck twins follow at 10 each.
Are radio telescopes included?
No. Radio dishes play a different game, so only optical and near infrared mirrors appear here.
Sources
- ESO ELT FAQ and facts (39 m mirror, current largest up to ten metres) and ESO construction proposal (ELT 39, TMT 30, GMT about 24 m)
- arXiv ELT era article (GMT 25.4 m surface, TMT 30 m, ELT 39 m) and Wikipedia ELT table (39.5, 30.0, 24.5 m)
- Observatory specs: GTC 10.4 m, Keck twin 10 m, Subaru 8.2 m, VLT 8.2 m UTs, Gemini twin 8.1 m, Magellan twin 6.5 m, MMT 6.5 m, Hale 5.1 m
Last verified: 2026-10-02 · 11 entries
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