Mobile now represents 20.3% of overall Facebook ad spend, with Google’s Android dominating the market in terms of smartphone spending.

The findings come from a new report by Kenshoo Social that analysed more than 2m Facebook ad clicks and conversions by global advertisers.

It found that the average cost per click on mobile ads (including both smartphones and tablets) is $1.38, 70% more than desktop ads at $0.81.

Looking at the breakdown by devices, Apple iOS dominates the tablet market with 97% of ad spend, but the opposite is true on smartphones where Android accounts for 71% of ad spend.

Assuming these figures are accurate, it shows that Facebook is still struggling make money from its hugely popular mobile apps.

According to its own stats, Facebook has 1bn active monthly users, of which 604m used its mobile products. 

We reported in September that Facebook had begun mobile ad network trials, and personally I’ve noticed more Sponsored Stories popping up in my timeline in the past few weeks (particularly for spread betting apps).

But if these initiatives still account for just 20% of overall ad spend, it suggests that the social network still has a long way to go before mobile is pulling its weight in terms of ad revenue.