I absolutely love finding and photographing the most tiny of mushrooms, I use my iPhone and a macro lens attachment called an Olloclip. It is hard to convey how tiny some of the mushrooms I photograph are, so here is a rough scale on my hand in centimeters for reference. I have labeled an estimate of each mushroom’s size below its photo.
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Cap 1.5 cm across
Cap is 0.25 cm, the stem is the same thickness as a horse hair.
Mushrooms are both less than 1cm in length, caps are 0.25 cm. They are growing from an older dead mushroom.
Cap is 1.5 cm across, the section pictured is approximately 0.75 cm wide.
This mushroom stands 0.75cm tall
Mushroom height is 1cm
Cap is 0.5 cm across, mushroom is 1.5cm in total height.
The of this Bird’s Nest Fungi is 0.5 cm. across. Each peridiole (small circular structure) is less than a quarter cm wide.
The smaller of these mushroom caps are approximately 0.5 cm in width.
Cap is 1 cm across.
The shorter mushroom is approximately 0.75 cm tall. 
Cap of mushroom is 1 cm wide, the slug is about half a cm long. 
Entire mushroom stands only 0.25 cm tall, possibly the smallest mushroom I have photographed. 
Each mushroom disc averages 0.25-0.5cm in width.
Mushroom is 1.5 cm across the long way.
Section of stick (with lichen on it) pictured is approximately 1.5 cm long, making the small orange fruiting bodies smaller than 0.25cm each.
This lichen stands about 1.5cm tall.
Cap is 0.5 cm tall.
Entire mushroom length is 1cm, cap approximately 0.5 cm in height, this proves a proper hat or hairstyle can make you look taller.
Average mushroom cap width, 0.5 cm. 
0.75 cm across.
The tallest stands 0.5 cm tall.
The average size of the top of these slime mold structures is about 0.2cm
Mushroom cap is 0.5 cm across, imagine how small that makes each of the spines hanging down.
Section pictured is approximately 1 cm wide.