Douglas-fir vs cedar

Douglas-fir is the framing wood; western redcedar is the siding and decking wood. Douglas-fir is about twice as hard, while the cedar is lighter, moves less and resists decay.

Coast Douglas-fir is about 103% harder than western redcedar.
Coast Douglas-fir is about 50% heavier than western redcedar.
Coast Douglas-fir has about 14% more movement across a flatsawn board than western redcedar.

Each column is the species its page leads with: coast Douglas-fir for Douglas-fir, western redcedar for western red cedar.

Side by side

Property	Douglas-fir	Western red cedar
Janka hardness, 12% MC	710 lbf	350 lbf
Weight, 12% MC	33.6 lb/ft³ (538 kg/m³)	22.4 lb/ft³ (358 kg/m³)
Specific gravity, 12% MC	0.48	0.32
Tangential shrinkage	7.6%	5.0%
Radial shrinkage	4.8%	2.4%
12 in flatsawn board, 6% → 12% MC	0.192 in	0.168 in
12 in quartersawn board, 6% → 12% MC	0.119 in	0.08 in
Bending strength (MOR), 12% MC	12,400 psi	7,500 psi
Stiffness (MOE), 12% MC	1.95 million psi	1.11 million psi
Crushing strength, 12% MC	7,230 psi	4,560 psi

One source: USDA Forest Products Laboratory, the authority for species properties it measured

Wood Handbook Tables 5-3b, 4-3 and 13-5; weight and movement worked with its Eqs. 4-14 and 13-3. A dash means the Handbook prints no value.

What sets them apart

Decay: Western redcedar heartwood is very resistant to decay. The Handbook gives Douglas-fir no such rating in its description. (Wood Handbook, p. 2-11 to 2-17)
Strength: Douglas-fir varies widely in weight and strength; use the denser wood where strength matters. Western redcedar is light, moderately soft and low in strength as a beam or post. (Wood Handbook, p. 2-11 to 2-17)
Uses: Douglas-fir goes into building lumber, beams, plywood and millwork. Western redcedar goes into shingles, siding, decking, greenhouses and boats. (Wood Handbook, p. 2-11 to 2-17)

For any other pair, open each species page from the wood hub; every page uses the same layout and the same sources.