Guide
What size circular saw do you need?
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In short
Choose by the deepest cut you need. A 165 mm saw cuts about 55 mm deep at 90 degrees, enough for sheet goods and decking. A 184 mm to 190 mm saw cuts about 62 to 67 mm, enough for most 2x studs. A 210 mm to 235 mm saw cuts about 70 to 85 mm for thicker timber, and a 100 mm cut needs a large beam saw. Depth drops at 45 degrees.
Products for this job
Compare all 8 productsMakita DHS660RTJ: brushless saw kit, 2 x 5 Ah
Check price on AmazonAffiliate linkBosch GKS 18V-57-2 GX: rail ready saw in L-BOXX
Check price on AmazonAffiliate linkDeWalt DCS572N: 184 mm brushless saw with brake, bare
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Circular saws are sold by blade diameter, but what really matters is cutting depth. Too small and you have to flip the timber and cut from both sides; too big and you carry a heavy saw for jobs a smaller one could do. This guide shows typical depths for each size and which size suits common UK jobs.
Blade size and cutting depth
Cutting depth is roughly a third of the blade diameter, minus the arbor and base. Check the spec for each saw, as the same blade size can give a few millimetres difference.
| Blade | Depth at 90 degrees | Depth at 45 degrees | Common use |
|---|---|---|---|
| 140 to 150 mm compact | About 40 to 50 mm | About 30 to 35 mm | Thin sheet, laminate |
| 165 mm | About 55 to 57 mm | About 40 mm | Sheet goods, decking |
| 184 to 190 mm | About 62 to 67 mm | About 45 to 50 mm | Studs, joists, most framing |
| 210 mm | About 70 to 75 mm | About 50 to 55 mm | Thicker timber |
| 235 mm | About 80 to 85 mm | About 60 mm | Sleepers, heavy framing |
| Large beam saws | 100 mm and more | Varies | Beams and posts |
165 mm saws
These compact saws are light and easy to control, and many run on 18 V batteries. They cut 18 mm plywood, OSB, MDF and decking boards with ease, and many fit guide rails. They are a good first saw for DIY and kitchen or flooring jobs.
They cannot cut a 75 mm thick timber in one pass; you would need to cut from both sides.
Their light weight is a real benefit for overhead and one handed positioning, and for long sessions breaking down sheet goods. If most of your cutting is 18 mm and 25 mm material, a 165 mm saw is often the most comfortable choice.
184 mm and 190 mm saws
This is the all round size. Depth around 62 to 67 mm covers 47 mm studs and joists, decking joists and most framing timber in one pass, even with some bevel. Cordless 190 mm saws with brushless motors are common on site, and corded versions are widely available.
If you are building a shed, a stud wall or a deck frame, this is the size to look at.
The trade off is weight. A 190 mm cordless saw with a 5 Ah pack is noticeably heavier than a 165 mm model, so think about whether you will mostly cut thick timber or mostly sheets. Blades in this size are widely sold in many tooth counts, which makes it easy to fit a fine blade for plywood and a coarse one for framing.
210 mm and 235 mm saws
Larger saws cut deeper for railway sleepers, thick posts and heavy joists. They are heavier and usually corded or twin battery. For very thick beams, specialist beam saws or a chainsaw may be needed.
See corded vs cordless circular saw for the power trade offs.
What about plunge and track saws?
Plunge saws typically use 160 mm to 165 mm blades with around 55 to 57 mm depth, but cut slightly less on a rail because the rail adds a few millimetres. They excel at long straight cuts in sheet goods. See circular saw vs track saw and our plunge saw guide.
If you need both precision in sheets and depth in timber, a 190 mm saw that accepts a rail can be a good compromise.
Choosing your size
List the thickest material you will cut and the bevel angle you need. Add a few millimetres so the blade clears the board, then pick a saw whose depth at that angle covers it. Do not forget blade availability: common sizes are easy to find in different tooth counts. See mitre and circular saw blades explained.
Set depth so the blade just clears the board, which reduces kickback risk; see circular saw kickback.
Note:Use only blades of the diameter and bore your saw specifies, rated for at least its speed. Disconnect power before changing blades or adjusting depth.
Frequently asked questions
What size circular saw for decking? A 165 mm saw cuts decking boards easily. For joists, a 184 mm to 190 mm saw is better.
Can a 165 mm saw cut a 2x4? Yes, a standard 47 mm thick stud is within its depth at 90 degrees.
Which circular saw cuts 100 mm deep? A large beam saw or specialist saw. Standard hand held saws stop around 85 mm.
Is a bigger circular saw better? Only if you need the depth. Smaller saws are lighter and easier to control.
What you need
- Check price on AmazonAffiliate link
Makita DHS660RTJ: brushless saw kit, 2 x 5 Ah
- Check price on AmazonAffiliate link
Makita DSP600ZJ: 36 V plunge saw with 2 x 5 Ah and rail
- Check price on AmazonAffiliate link
Evolution R255TBL+: 255 mm, 85 mm deep, rack and pinion fence