What Size Angle Grinder Do You Need: 115, 125 or 230mm

An angle grinder is sold by its disc diameter, and the UK shelf carries three: 115mm, 125mm and 230mm, or four and a half, five and nine inches. The diameter sets how deep the tool cuts and how fast the disc may turn; everything else follows. This guide sizes the work against figures Makita UK, Bosch Professional UK and HSE publish, then maps the seven picks in our top 7 angle grinders ranking onto the sizes. Nothing here is bought or handled; where a figure is arithmetic on a published one, it says so.

115mm is the UK default

115mm is the size the UK shelf is built around: it is what Screwfix, Toolstation, B&Q and Wickes stack their cutting, grinding and flap discs in, and five of our seven picks take it. Klingspor lists 100, 115, 125, 150, 180 and 230mm as the common diameters, but the UK maker pages cited below jump from 125 to 230. And the 7-inch grinder? Seven inches is 180mm, a real size but not one the UK market is organised around. The big UK grinder is the 9-inch, 230mm.

What the disc diameter actually sets

Depth of cut comes from radius, and the spindle, flange, nut and guard eat most of it. Makita UK publishes a maximum depth of cut for its corded grinders, and the ladder is the argument in three numbers: 30mm on the 115mm GA4530R, 35mm on the 125mm GA5030R, 68mm on the 230mm GA9020. Einhell publishes 28mm for both of its 115mm grinders in our ranking. Derived from those figures rather than printed by anyone: a little over a quarter of the diameter is usable cut. So 125mm buys 5mm of depth, not a different class of tool; Makita publishes the same 720W, 11,000 min-1 and 266mm length for the GA4530R and GA5030R. Buy against the published depth, not the diameter.

Spindles, bores and why a 125mm disc must not go on a 115mm guard

Every grinder cited here has an M14 spindle, at all three sizes: Bosch Professional publishes it for the GWS 7-115 and GWS 22-230 P, Makita UK for the GA4530R, GA5030R and GA9020, and Makita's manual for the DGA454Z in our ranking. The bore is 22.23mm on all three Makita sizes, so a 125mm disc, or a 230mm one, threads onto a 115mm grinder without resistance. HSE's abrasive wheels guidance, HSG17, says what does the protecting: a guard contains the pieces when a wheel bursts, keeps the operator off the wheel, and has a stated secondary job of preventing an oversize wheel being fitted. On a portable machine it sits between wheel and operator and clears a new wheel's edge by no more than 6mm. HSG17 records serious, often fatal, accidents where a guard was removed to mount an oversize wheel, which then ran faster than its maker allows. A 115mm guard is built for a 115mm disc. If you want 125mm, buy the tool built as a 125.

Speed and power by class

A 230mm grinder turns slowly for a reason. Discs are rated by the speed of their edge, and the usual rating for cutting discs is 80 m/s. Klingspor converts it to 13,300 rpm at 115mm, and HSG17's speed table carries the conversion down the sizes: 12,250 rpm at 125mm, 6,650 at 230mm. The corded 115mm class here runs 720 to 750W at 11,000 to 12,000 rpm; Makita's 125mm GA5030R is 720W at 11,000 min-1; the 230mm class is 2,200W at 6,500 to 6,600 rpm on Bosch's GWS 22-230 P and Makita's GA9020. A 230mm disc on an 11,000 rpm body would have its edge doing about 132 m/s, by arithmetic. The 18V picks are 115 and 125mm only: Makita's DGA454Z and Einhell's TE-AG 18/115 publish 8,500 min-1, Bosch's AdvancedGrind 18V-80 a preselection from 2,800 to 12,000 rpm, and DeWalt UK no speed at all for the DCG407N-XJ. The 230 is a corded, two-handed tool: Makita publishes 5.8 to 7.9kg for the GA9020 and Bosch 5.5kg for the GWS 22-230 P, roughly three times the 1.8 to 2.2kg of the 115s, and both fit a switch that stops the tool when released.

Jobs by size

• Paving slabs, kerbs, block paving. Measure the slab against the published cut, 30mm for a 115 and 35mm for a 125. Anything thicker means scoring and snapping, or cutting from both faces and living with the step. A 230 at 68mm has more than double the reach: this is the job that justifies one, and the one most DIYers would rather hire for.
• Chasing walls, cutting brick and block. A 115 with a diamond disc; a chase is shallow, and the small tool is the one you can hold steady on a wall. Dust is the real problem, which is why the GWS 7-115 taking Bosch's extraction attachment counts for more than its wattage.
• Rebar, angle iron, threaded rod, seized bolts, box section. A 115 with a thin metal cutting disc. Size up to 125 only if you are regularly through section thicker than 30mm.
• Sharpening, rust, flap-disc sanding, weld dressing. Any size, and the small ones are easier to control. Speed matters more than diameter here, which is what the AdvancedGrind 18V-80's preselection is for.

The safety points UK guidance makes

HSG17 is written for workplaces under PUWER 98, but its precautions are what keep a DIYer out of A&E.

• Guard on, always, between you and the disc, sized for the disc it came with, and the closed cutting guard for cutting discs.
• Match the speeds. Every wheel over 80mm carries its maximum speed in rpm and m/s, and the speed marked on the machine must not exceed it. Overspeeding is one of the main causes of wheel breakage, and stress in a wheel rises with the square of its speed.
• Reinforced cutting discs only, and never for grinding. Unreinforced cutting-off wheels never go on a portable machine, hand-held wheels carry a three-year use-by date, and grinding on the side of a thin, straight-sided wheel is dangerous.
• Mounting is a trained job, on the machine the wheel was intended for, after inspecting it for damage.
• PPE. Eye protection to BS EN 166 and dust masks to BS EN 149, with head, hand and foot protection on site.
• 110V on site. HSG17 says the preferred voltage for these machines on construction sites is 110 volts, with an RCD if 240V has to be used; HSE's 2023 HSG141 puts battery tools first, 110V for power tools, and 230V only where nothing else will do. Makita marks 110V with /1 and 240V with /2, DeWalt appends -LX, and Bosch Professional lists the GWS 7-115 in both. A 110V tool will not run from a domestic socket without a transformer.

Which of our picks fits which size

None of the seven is a 230: two are 125mm, five 115mm.

125mm, cordless. The DeWalt DCG407N-XJ 18V XR Brushless 125mm Angle Grinder (Body Only) is for anyone who wants the extra depth and already runs 18V XR packs: brushless, and the only grinder here that publishes a brake, plus a kick-back brake and an E-Clutch that cuts the motor when the disc binds. The Bosch AdvancedGrind 18V-80 125mm Cordless Angle Grinder (Home & Garden, Body Only) is the green Power for All version: preselection from 2,800 to 12,000rpm, soft start, a tool-free clamping nut, and no motor type, power figure or brake published.

115mm, cordless. The Makita DGA454Z 18V LXT Brushless 115mm Angle Grinder (Body Only) runs 8,500 min-1 on an M14 spindle with an automatic speed change under load and the Active Feedback cutoff, but no brake. The Einhell TE-AG 18/115 Li-Solo 18V Power X-Change 115mm Angle Grinder (Body Only) is the brushed 8,500 min-1 tool with a 28mm published cut, soft start, restart protection and the deepest owner record in the category by a distance. Both are body only.

115mm, corded. The Bosch Professional GWS 7-115 720W 115mm Corded Angle Grinder (240V) is the blue Professional workhorse: 720W in, 300W out, 11,000rpm, M14, 1.9kg, restart protection and a flat gear head. The Bosch UniversalGrind 750-115 is the green Home & Garden equivalent at 750W and 12,000rpm with three cutting discs in the box. The Einhell TC-AG 115/750 750W 115mm Corded Angle Grinder matches that 750W and 12,000 min-1 and publishes a 28mm cut and a restart safeguard.

Common questions

Can I put a 125mm disc on a 115mm grinder?

Not with the guard it came with. Spindle and bore match, and at 11,000 to 12,000 rpm its edge would even stay inside an 80 m/s marking by arithmetic. The guard is the problem: it is sized to the disc, HSG17 wants no more than 6mm of clearance, and it counts removing a guard to fit an oversize wheel among the causes of fatal accidents. If you want the 125, buy the 125.

Is a 9-inch grinder too big for DIY?

As a first or only grinder, yes. A 230 weighs 5.5 to 7.9kg by the Bosch and Makita figures against 1.8 to 2.2kg for a 115, needs both hands and 2,200W, and exists for one class of job: getting 68mm into slab, kerb and thick section. If a patio is the only reason, hire the 9-inch for the weekend and own the 115.

What size angle grinder for cutting paving slabs?

Measure the slab against the published depth of cut: 30mm for a 115 and 35mm for a 125 by Makita's figures, 68mm for a 230. A handful of cuts: score and snap with the 115 you own, or hire a 230 for the day. A whole patio, block paving or kerbs: the 230 with a diamond disc, and the dust mask HSG17 asks for is not optional.

Sources

• HSE, Safety in the use of abrasive wheels, HSG17 (third edition, 2000).
• HSE, Electrical safety on construction sites, HSG141 (second edition, 2023).
• Makita UK, GA4530R product page, and the GA5030R page on the same site.
• Makita UK, GA9020 product page.
• Bosch Professional UK, GWS 7-115 product page, and the GWS 22-230 P page on the same site.
• Klingspor UK, Maximum operating speed and its angle grinder page.