How to drill a hole in glass
Glass cracks for the same three reasons every time: the wrong bit, too much speed, and running dry. Get those right and a mirror, a bottle, or a window pane takes a clean hole. This page covers the two bit families that work, the speeds, the water discipline, the starting technique, and the one kind of glass that cannot be drilled at all. Every claim cites two or more named sources.
Three things to know before you start.
- Two bit families work: diamond-grit bits (solid tip or hollow core) and carbide spear-point glass-and-tile bits. Twist bits and masonry bits shatter glass [1] [2].
- Slow and wet is the whole method. Under about 1,000 RPM on a full-size drill, with water on the cut at all times [3] [4].
- Tempered glass is off the table. It shatters when drilled; holes must exist before tempering [5] [6].
Step 1: the right bit
Glass is ground, not cut. Diamond-grit bits, solid-tip for small holes and hollow core bits for larger ones, do exactly that, and they are the precision-and-life choice [1] [7]. Carbide spear-point bits, sold as glass-and-tile bits, handle small holes in ordinary glass; Bosch's GT sets run 1/8 to 3/4 in [2] [8]. Dremel's glass bits are diamond-impregnated in 1/8 to 1/4 in for rotary tools [1] [9].
| Bit family | Hole sizes | Best for | Sources |
|---|---|---|---|
| Carbide spear-point (glass-and-tile) | about 4 to 14 mm | Small holes in ordinary glass and tile | [7] [8] |
| Diamond solid-tip | under 1/4 in | Small holes, harder glass, longer life | [7] [1] |
| Diamond hollow core | 1/4 in to over 1 in | Larger holes in panes, bottles, mirrors | [7] [10] |
Row sources: [7] Drillbitsworld's glass drill bit guide (spear-point bits most common for 4 to 14 mm holes; diamond for larger), [8] Toolstash's Bosch GT2000/GT3000 set listing (carbide spear points 1/8 to 3/4 in), [1] Dremel's 663DR glass drilling bit page (diamond-impregnated, for glass, bottles, tile), [10] BaseballRuler's diamond hole saw set specs (10 sizes, 1/4 in upward for glass, bottles, stone).
Step 2: the right speed
Full-size drills run glass bits slow: under about 1,000 RPM, with small bits in the 300 to 600 RPM neighborhood and larger cores slower still [3] [4]. Bosch's own testing guidance for its glass-and-tile bits reports best results below 1,000 RPM with water [3]. On a cordless drill, that means the lowest gear and light trigger pressure.
One honest exception: tiny rotary-tool bits. Dremel rates its 3.2 mm diamond glass bits at 10,000 to 15,000 RPM, because the bit diameter and the pressure are both very small [9]. That figure is from the manufacturer's own pages only, so treat it as Dremel's specification for Dremel bits, not a general license for speed.
Step 3: water, constantly
Dry drilling cracks glass and destroys diamond grit. Keep the cutting point wet the entire time: a drip bottle, a spray mist, a sponge, or a dam of plumber's putty or modeling clay ringed around the spot to hold a pool of water [4] [11]. Dremel's instructions say the same in fewer words: apply cooling liquid, and keep applying it during drilling [11]. If you see dry powder or steam, you have already gone too dry; stop and rewet.
Step 4: the starting technique
The bit's tendency is to skate on the smooth surface, and everything in the method exists to stop that.
- Tape the spot. Masking or painter's tape over the mark gives the bit grip and a visible target [4] [11].
- Start at about 45 degrees. Tilt the drill until the bit bites a crescent groove, then gradually raise it to 90 degrees [11] [4].
- Light, steady pressure. Let the drill's weight do most of the work; excess pressure heats and cracks [11] [3].
- Support the glass. Flat on a padded or plywood surface; a sacrificial board under the exit side prevents back-face chip-out [4] [12].
- Ease the breakthrough. Reduce feed as the bit nears the far side; punching through hard blows out the back [4] [12].
The one rule with no workaround: tempered glass
Tempered (toughened) glass cannot be drilled, cut, or notched after tempering. Vitro's fabrication bulletin, backed by ASTM C1048, states it flatly: all fabrication must happen before heat treatment [5]. The tempering process puts the pane's surfaces in compression and its core in tension; breaching the surface layer releases that stored stress and the pane goes to pebbles [6] [5]. No bit, speed, or cooling scheme makes post-tempering drilling reliable, and attempts void warranties [6].
Identification before drilling: look for the etched tempering stamp in a corner (the "bug"), or check for stress patterns through polarized lenses; if still unsure, ask the supplier [6] [5]. Shower doors, car windows, glass tabletops, and most patio door panels are tempered; wine bottles, mirrors, and window panes generally are not.
Common jobs, one line each
- Wine bottles and jars: diamond core bit, bottle clamped or nested in a V-trough, water dam on the glass, lowest gear [10] [7].
- Mirrors: drill from the front with the reflective face supported full-length on plywood; back chipping ruins a mirror visibly [4] [12].
- Window panes: confirm it is not safety or tempered glass first, then spear point or small diamond tip with the tape method [6] [4].
- Glass tile and backsplashes: same bits and water discipline as tile; the full tile treatment is our how to drill into tile page.
Related guides
Also on this site: how to drill into tile without cracking it for the ceramic and porcelain counterpart, drill bits by material for the full bit-family picture, and the drill speed chart for RPM targets in every other material.
Sources
- Dremel US, 663DR 1/4 in Glass Drilling Bit product page (diamond-impregnated bit for glass, bottles, tile; recommended speeds): dremel.com
- Toolstash, Bosch Glass and Tile Bit Set GT2000/GT3000 specs (carbide spear-point bits 1/8 to 3/4 in for glass and tile): toolstash.com
- Toolstash, Bosch GT100 glass and tile bit test (best results under 1,000 RPM with water; low speed, light feed): toolstash.com
- SensibleDigs, How to Drill Holes Through Glass (small spear bit about 400 RPM or below; 1 in diamond core about 500 RPM; tape, 45-degree start, ease off near breakthrough): sensibledigs.com
- Vitro (formerly PPG), technical bulletin TD-124, fabrication of heat-treated glass (cutting, notching, and drilling cannot be performed after tempering, per ASTM C1048): vitroglazings.com
- Glass Railing Store, Can You Drill Tempered Glass (any attempt risks total shattering; holes must be drilled before tempering; bug stamp and polarized-light identification): glassrailingstore.com
- Drillbitsworld, Glass Drill Bit Guide (spear-point bits most common for 4 to 14 mm holes; diamond for larger holes and harder glass): drillbitsworld.com
- Bosch, glass and tile bit sets GT2000/GT3000 (carbide spear points for glass and tile, 1/8 to 3/4 in), via Toolstash: toolstash.com
- Dremel GB, Glass Drilling Bit 662 (recommended speed 10,000 to 15,000 RPM, 3.2 mm): dremel.com
- BaseballRuler, diamond hole saw set specs (10 sizes from 1/4 in for glass, bottles, stone): baseballruler.com
- Dremel GB, official how-to for glass drilling bit 662 (hold tool at 45 degrees to enter, then lift to 90; secure the workpiece; apply cooling liquid, re-apply during drilling; no excessive pressure): dremel.com
- Lowe's, How to Drill a Hole in Glass (plywood surface, low speed, backing to prevent chip-out): lowes.com